I just read where JJ was going to initial kill off Poe, and had even hired the actor with the actor knowing that the character was getting killed off. Then, JJ reconsidered, apparently, and told the actor that he was going to change some stuff and the actor was going to be in the full movie.
So, it would seem that Poe isn't part of some larger plot, unless JJ completely redid big plot aspects very late in the process.
Characters' story lines get changed all of the time. It probably depends on what Rian Johnson wants to do with him.
Oscar Isaac had kind of blown up since Star Wars started casting. That could be good or bad. They may want him to stick around for a little star power (a la a new Harrison Ford), or they may want to save a little money. He's probably going to command a lot for fairly little screen time.
I mean, if he's just going to be a glorified Wedge, then cut him. But he was a pretty witty, entertaining character that they can get some use out of, so if they choose to expand his role, I think it would be good for the films. He seems like the kind of guy Rian Johnson, specifically, could get some mileage out of.
I think the challenge with this trilogy is that the first one dealt primarily with Han Solo, Luke, and Leia. Vader just popped in as an antagonist; there wasn't a lot of character development for him until ROTJ. I just don't think there's going to be a lot of room for "Poe-as-Han" in this series because they really want to (rightly) dive into Kylo/Ben.
Which is great because Adam Driver is great, the character is great, and the potential for the continued conflict with Rey is going to be fantastic. That girl was a badass.