Shot down a light scout, went to investigate.
These two images illustrate nicely:
I have seen a sebillian take:
5 shotgun shells
6 Assault rifle rounds
12 machine gun rounds (both man and vehicle carried)
and a plasma pistol bolt (one of his buddies reaction fired and hit him)
These are only the shots that hit and he cried out in pain from.
This was all in one round.
He did not die.
I know their xenopedia entry says they are tough, but that tough?
I loaded the autosave, there were more sebillians, and invulnerable again.