Most Helpful Guy
Well, if you pay close attention, you can see that the walkers are tearing open Nicholas, not Glen. Also, he wasn't mentioned in the "In Memorium" recap, as well as, the answer as to the "is he dead?" question keeps being avoided by the network overall; This didn't happen at all when Dale or Hershal died. It was publicly and formally announced that they were dead.
Although, when Carol's daughter Sophia went missing, it wasn't known what became of her, until a few episodes later; in which they found her among the dead in Hershal's stash of walkers.
Who knows what happened to him (the writers know), that's the awesomeness that is, The Walking Dead.