What plot points did a movie just not bother resolving?

[bhireg000]

I was re-watching Back to the Future the other day, and realized that we never found out what happened to the Libyan terrorists after they shot Doc Brown. Did they all die in the car crash? And if they're still alive what's stopping them from trying to go after Doc Brown again once Marty got back to the future? According to the wiki, this was actually answered in the novelization (they were arrested), but movies should stand on their own, and if the movie doesn't address it then it doesn't count.

So what other plots did you notice that a movie introduced but then left dangling?