One of the players is most likely retiring his character from the game. Thing is, he's the only Awakened character.
Sure, he was only an Adept, but it was the only Magic the team had-- I didn't mind, and I didn't throw tons of Magical encounters at them as a result. It was refreshing, but now I can't just pretend their enemies aren't sending Spirits out anymore.

My big worry is really just Astral perception. How can they prevent Spirits from just followin' em around all day, reporting to daddy, who happens to be the team's arch-rival? Or how do I prevent them from stumbling into a facility being watched by four Spirits, without even giving them a -chance- at knowing? So on.

I guess the most likely answer is "You can't", but I figured I'd try anyway.

Edit: I'm the GM, if it wasn't obvious.

I think you've put your finger on some reasons why Mages are essential components of any team expecting to survive in the Shadows of the 6th World. Though, unless your Adept had Astral Perception, there's no change... and they could never have offensively dealt with the following spirits on the Astral even if the Adept could see them...

Remember, though, that stealth works against astral perception too. Your mundane runners are only throwing shadowy reflections onto Astral sight, and so can sleaze off behind other shadowy reflections... It's not like they have the auras of quickened/sustained spells haloing them. Watchers are *dumb* and easy to hide from. Heck, if the party split up, there's a chance the watcher will get confused; some standard tradecraft to ditch tails would probably throw off that sort of Astral surveillance. If the opposition Mage uses a bound spirit to track them, that's a service, and if they use an unbound spirit, it means they can't have one right where they are, and the one they've got tracking won't come back cos it's on Remote.

He did have Astral Perception, which was my only concern, really.

The rest of your reply puts my fears to rest-- it's hard for me to 'perceive' the Astral as a GM not entirely acquainted with the Magic rules; in fact, your comment on Watchers being 'dumb' really makes me re-visit a few previous decisions. I've been trying to solidify my position for a while now, and I think that makes a lot of sense. Thanks.

Arsenal introduced many gadgets that teams with no Astral characters can use to deal with magic situations. As a GM, just give them fairly easy access to these items, and you'll be able to still include magical components into your games. A good way to start them off is for them to be hired by a Johnson that says "I know your team doesn't have a mage, so here, take these items, they will come in useful". From a Johnson perspective, it also makes sense because giving the team some gear is cheaper than hiring a mage anyway.

Remember though this is SR. They're in a connected world. You might want to give them the chance to go out and shop around for a mage or an adept with astral perception and an astral ranged attack.

They might actually have fun with it. Though it's obviously harder to find mages that other runner types.

Like Mr. Sunnyside said you can sub-contract out any job that a team might need done. It would simply cost them a bit of nuyen.

They can also be hired for runs where no mage support should be required (runs in areas with high background counts, run against an opposition that doesn't rely on magic).
Also consider that a lot of magic securities are passive (they just block mages, like wards) or limited to magic threats (a spirit can be ordered to look only for projecting mages). Most places can't afford too many patrolling spirits, so the few available should restrict their actions to magic threats the same way a spider will rather be watching his own system rather than try to hack intruder's PANs.

Furthermore, spirits aren't from this world. Even the more intelligent spirits might not be able to tell if someone should be here or not just by looking at the way they're dressed or behave. The only way I can see for them to be able to tell if someone is an intruder or not would be if they were shown the aura all people who should be there and told to report (or deal with) when other people are seen inside the building. Please note that such security procedures are quite cumbersome (every visitor should be shown to the spirit to avoid problems) so they should be pretty rare.

Finally, it's still possible for the team to find a way around. For example if the team has to to a B&E on a building that's probably guarded by spirits, they'll have to look for information about that spirit protection to know if that's a concern to them. If it is, they'll just need to either incapacitate the summoner so that the spirit will be released or have a legitimate cover so that the spirit won't mind them.

Living beings are just as visible on the astral as a quickened spell.
It's inanimate objects that only have a shadowy presence on the astral.
Astral stealth is tricky at least and works by completely other means than physical stealth.
Hiding in crowds or dense vegetation works, but in mostly lifeles areas, a perfect physical hideout can be completely useles on the astral.
On the other hand, getting into structures that block LOS to your aura is extremely useful.

High intuition and perception scores help to sense passing astral presences or ritual magic coming in (good look without assensing, though).

As has been mentioned, Arsenal has some useful manatech to help the team out of the worst problems,
glow wands and petit brume grenades being the preferred choices.

Hiring a mage to ward a hideout for the group can be helpful, too.

Maybe they can pay a magician to summon a spirit, bind it (so it exists until its services run out instead of sunrise/sunset), and lend its services to one of the characters.

You can then play the spirit as an NPC - give it a personality.

If the party likes the spirit, they can pay to rebind it and get more services.

If the party doesn't like that particular spirit, they can pay for a new one.

A Spirit of Man with Detect Enemies or Detect Magic plus its regular powers might be good. Play it like a soldier ("Sir, yes, sir.") a peon ("Yesh, me lord.") a butler (English accent) or genie. I don't know if it's legal, but a service could be something like "use Detect Magic and inform whoever is holding your lamp of any magical activity occuring within range."

Well, if an astral entity passes through them, they get a chance to detect it.

Also, having spirits follow people around is expensive - either the mage blows a service of a bound spirit to do it, or their only unbound spirit is tied up on a remote service that wipes any remaining services owed.

Wait, why not? Maybe the spirits are tired of getting pwnzered. Maybe they had a special attraction to that adept. If you feel a need to explain the absence of spirits, let them have a nasty session where the spirits are giving them a hard time, then have them encounter a mysterious person (free spirit) who makes the spirits leave them alone.

Or just don't explain it. Mystery is interesting.

Remember, Astral Space is subject to extraterritorality. So if Corp A sends a spirit out to trail the runners, and they decide to walk into the Renraku owned shopping mall in Snohomish, then if the spirit follows, Corp A has just violated Renraku's extraterritorality... and I do believe, Renraku might just get pissed at that... (and even if it isn't a corporate-summoned spirit, do you think Renraku is gonna let some "uncontrolled" spirit wander around their mall?)

Alternatively, have them go through a ward and out the otherside. Wards aren't just for high-class corporate zones, either. The Mafia gambling den in the barrens probably has one. The street doc in the barrens may have one (don't want those Shedim to bug him while he's chopping up someone who didn't make it). Regular hospitals probably have them. Good safehouses probably have one. Etc, etc.

Finally, have them discover some areas with a high background count or aspected astral space. The barrens, again, probably will suffice for background count, or a prominent church may count for aspected space. A hospital is likely to have a background count as well (just walk through the emergency room, eh?) A background count of 3 will disrupt any force 3 spirit, and background count affects astral visibility, so higher force spirits, even if they are willing to pass through, probably will lose the runner's trail.

If one of your players is willing, allow them to purchase the Astral Sight positive quality for karma. Maybe they are just now slowly Awakening? There's also that Latent Awakening things that I know possibly nothing about.

Their subcontracting could be as simple as giving some magic 1 guy 50 cred to astrally watch them walk by on the street to see if anything is following them.

Or get a dual-natured, attack trained guard dog.

Okay, that would be kinda inconvenient in a AAA zone, i admit.