Is line of sight needed to sustain a spell?

Example: Once Physical Mask is cast and sustained on a teammate, can the mage then go home, and the teammate will still have the spell in effect on him?

No...

Yes... Your example is correct.

I would rule that if the player went through an astral barrier, there might be some issue; "Cutting off the mana" or somesuch. I don't have a rule that applies to though.

-DrZ

Just like any other spell that interacts with a magical Barrier (Contested Rolls) of any type, of course.

My instinct was backed up by rules! A novel feeling.

-DrZ

No worries... It happens from time to time.

I looked through the rules (both 4th and 5th editions) and was unable to find anything that stated this plainly. Is there any section that someone can reference for us. Our problem is that our GM has a small bias against magic and tends to interpret the rules for magic as he reads them in the book.

Thanks

I can only remember, that in SR4 it was explicitly stated for critter powers, that they don't need LOS anymore after being "cast" (established).

For SR4 you had it indirectly by (page 203, under Range, emphasis mine)
All spells have a range at which they can be cast. For most spells, the range is line of sight(LOS). If the caster can see the target, regardless of distance, it can be affected.

The corresponding paragraph in SR5 about Range on page 282 also only writes about range (like LOS) being important for casting, not any mention of sustaining.

Remember, that if a mage puts a spell on somebody and this somebody runs around elsewhere, the spell can relatively easily be tracked back to the mage (and the mage has to live with the sustaining penalties).
Who knows who will come visiting, if your mage hands out spells left and right.