Why would the vessel keep all the buffs, sans spirit? That's just begging for abuse. Don't the rules specifically say, 'this is identical to Possession', anyway?

First of all, it does not work. It is handled like possession and you can't posses vessels allready taken.
Second of all: The victim would be force on the astral plane (Bad for a human, not so bad for a spirit). So you posses the host and now you have a real angry spirit on the astral plane, wanting to kick you ass!

For example, the spirit with this power can ANNIHILATE the host spirit. In this case, an Insect Spirit. So it did.

Vessel Trading
Type: P • Action: Complex • Range: Touch • Duration: Instant
The spirit can use its Possession power to not only take over
a living vessel, but also to evict the victim’s life force from it, either
ejecting the victim out as an astrally projecting creature or putting
the victim’s life force in its old vessel. If the old vessel already
contains a (previously subdued by possession) life force, the new
victim may not be placed there, and is forced to astrally project instead.
Follow the standard rules for the Possession power (p. 101).
Victims placed into a vessel (living or inanimate) are not able to
control it like a possessing spirit—they are trapped there and typically
find the experience inexplicably horrifying. The only way
they may escape is if a free spirit with this power switches them
back, they are capable of astrally projecting and freeing themselves,
or the vessel is exposed to an astral rift or entity with the
astral gateway power. Victims trapped in an inanimate vessel or
astral space will feel their life force ebbing away, and will die after
(Magic or Essence) x 2 hours.

Vessel Trading
Type: P • Action: Complex • Range: Touch • Duration: Instant
The spirit can use its Possession power to not only take over
a living vessel, but also to evict the victim’s life force from it, either
ejecting the victim out as an astrally projecting creature or putting
the victim’s life force in its old vessel. If the old vessel already
contains a (previously subdued by possession) life force, the new
victim may not be placed there, and is forced to astrally project instead.
Follow the standard rules for the Possession power (p. 101).
Victims placed into a vessel (living or inanimate) are not able to
control it like a possessing spirit—they are trapped there and typically
find the experience inexplicably horrifying. The only way
they may escape is if a free spirit with this power switches them
back, they are capable of astrally projecting and freeing themselves,
or the vessel is exposed to an astral rift or entity with the
astral gateway power. Victims trapped in an inanimate vessel or
astral space will feel their life force ebbing away, and will die after
(Magic or Essence) x 2 hours.

If all of the boxes on a spirit’s Condition Monitor Track are filled
in, that spirit is disrupted and forced back to its home metaplane. Any
services still owed by the spirit are lost.

Since it isn't taking damage but the power explicitly states it causes the death of the victim, I think it is safe to say that the insect spirit in this case is toast.

Insect spirits don't count as Possessing the host, but Inhabiting by RAW. Also the spirits are merged so they count as one spirit not two for purposes of Vessel Trading.

Additionally since RAW states that it states that the spirit DIES (not counts as disrupted - it outright dies) this indicates on the few possible methods by which you could conceivably kill an insect spirit without actually having to go The Hive metaplane to deal with the spirit.

Arguably the insect spirit could (once ejected) try and invest itself into another host that might be prepared inside it's appropriate magical lodge but that wasn't a possibility in this instance. Given all the characters were under NPC control in this instance and the insect had nowhere else to go, he stated that the insect spirit would eventually die.

Also, to quote SR4A, p.186:


Since it isn't taking damage but the power explicitly states it causes the death of the victim, I think it is safe to say that the insect spirit in this case is toast.

There might be more specific rules elsewhere governing how you can actually kill a spirit properly but I'm tired and am going to bed. I think the above is sufficient evidence to prove that you're wrong though.

- J.

I have to agree with Irion here: as soon as the Insect Spirit is ejected from the host it is no longer bound by the rules for Inhabitation - namely, it regains Astral Form in the event of a Hybrid Form merge. It defaults to standard spirit rules, such as being able to persist in the Astral indefinately or being able to travel the metaplanes/using metaplanar shortcuts.

EDIT: The ability of a spirit to maintain their own Astral Form kind of removes the "trapped in... astral space" part.

Evanescence (Weakness )
Extraplanar entities suffer from a phenomenon known as Evanescence, an irresistible fading of form and Force if they remain in Earth’s astral space. Unfortunately, these beings have learned to counter such dissipation by anchoring
their astral forms to the physical plane, normally through the use of the Inhabitation or Possession powers. Extraplanar spirits can persist in the Gaiasphere for only a limited amount of time. Once a spirit has found its way to Earth’s astral plane (or was conjured, in the case of insect spirits), its astral form begins to dissipate. For each sunrise or sunset that a spirit with Evanescence remains in full astral form, its Force rating is permanently reduced by 1. If the spirit’s Force reaches 0, it dissipates (whether it is disrupted or permanently destroyed is unknown).
A spirit with this weakness that is bound to a magician, or that goes free, only loses Force at the rate of 1 point per week. As a side effect of Evanescence, the astral forms of extraplanar spirits are translucent and harder to detect. Apply
a –3 dice modifier to all Assensing Tests (see Astral Visibility, p. 114 and Astral Perception, p. 182, SR4) against any such spirits in full astral form. This insubstantial form also enables them to bypass astral barriers with greater ease (see Passing Through Barriers, p. 185–186, SR4). Apply a +3 dice pool modifier to the spirit for the relevant test. All effects of Evanescence are negated as soon as the spirit inhabits or possesses a vessel. If it is somehow driven out of the vessel, the spirit’s astral form starts to dissipate again.

@The Jake
So? In what way are you contradicting Neraph.

If the spirit is cast out of his vessel (Which is hard to say, because there are no rules about trying to posses an inhabited subject.) it is on the astral plane. There it may kick your ass for (lets say a good 2 hours) than it should go home, before it starts loosing force.

except to say the rules are open you can interpret it whichever way you want.

If basic literacy and comprehension are beyond you

I don't believe Neraph was considering Evanescence in the singular use case I was referring to.

Irion - I don't believe Neraph was considering Evanescence in the singular use case I was referring to. At which point, then it's fair to say - on any other occasion - you two might be right. Except in this one, it isn't clear. Secondly, I just quoted the exact rules that explain it. If basic literacy and comprehension are beyond you, then I dunno what else to tell you - except to say the rules are open you can interpret it whichever way you want. We interpreted it one way. Feel free to interpret it another. Just don't deign to tell me it's wrong because I've just proved it isn't black and white. I'm done arguing with this.

- J.

@The Jake
Beeing drained into nothing is quite a good motivation, even if you do not want to...

Every spirit can go back to his metaplane with a complex action.