I agree that it's bad writing if Glen lives, especially the way the scene was shot. There's zero chance he would survive with that many walkers chewing on anything alive (or recently dead) in the vicinity.
That said... I won't be disappointed if he's alive. I can forgive a little deus ex machina now and then, especially with so few likable cast members.
If he comes out unscathed, I'd be upset with the writing. I'm working on this assumption that Glenn is already dead this season, whether or not he survives this ordeal or not, he's a goner.
With the way they shot the whole thing, and with Daryl, Rick, Sasha and Abraham being on the other side, the only logical reason I could think of that could distract this horde is if a mystery character would eventually show up and do the distracting. Which would be both good, but at the same time, as a fellow poster mentioned, would be one of things that would make you say "I can't take threats to main characters seriously" from now.
Here's what I think would happen.
He gets out, but with bites. Knowing he's going down at any time, he'll find his way to Alexandria to see Maggie one last time, but he'll fail as the infection will kill him. As this is happening, the group will try to find him, and they eventually will, as a walker.
Maggie then breaks down. And she's going to have to put her down, because, she has to, right? But seeming as they already did this with Daryl and Merle, the writers would go a different path. Maggie would "attempt" to put Walker Glenn down, but instead she'll just let him eat her, as she has lost everything in her life. And someone will have to put Glenn down, and Maggie, bitten and mortally wounded, would have to be mercy killed as well.