All aboard, next stop: denial! There are lots of reasons people don't think he's dead so no worries.
1) he's glenn and his fanbase borders on cultish and it'd certainly be an interesting turn of events for the show if he was killed
2) he wasn't on the talking dead or the "In Memoriam" section they usually have
3) Nicholas fell with him and when the zombies were attacking, the way his blood pooled/entrails were shown they were too far up on his body, suggesting that it was Nicholas getting attacked instead of him.
4) TWD is all about those twists, there's probably a hole in the dumpster that he pulled himself under and up into.
5) If he was really dead, REALLY dead, why wouldn't they make that absolutely without a doubt clear?
Anyway, I was a hair away from breaking out in a sweat like ha ha they're gonna get out of this right? RIGHT? GUYS?
I personally don't think he's dead and they wrapped the episode up too neatly by making him seem dead and then fitting a 90-minute flashback episode between that one and the resolution where we find it out. Let's hope!