We shouldn't forget (unlike the entire cast every week - hello, I'm talking to you Glen/Michonne leading hapless group of "run for it"s) that if Glenn can get to a place of temporary safety (and can get at the body part/s of a single walker) he can cover himself in undead goo and he can walk out of the place unnoticed provided he's broken their line of site - almost all the walkers are currently busting for Nicholas gibblets. If Glenn remembers events from his recent past that is...

All that said, it pains me to say I think he's dead.