The poor sod is nowhere to be seen, but keeps drowning perpetually.
I didn't receive an escort message when entering Elvala, but had another rescue mission in the Scintillating Caves with a repentant thief. I have died in its course, dragging the poor fellow to the Eidolon and back, then delivering the guy to the portal safely. I don't know if it is related in any way and I don't remember the name of the SC's thief either.
Cheers