Re: Will there be a character's death in part 3?
Well I say Captain America. Chris Evans only has 2 more contracts left after shooting Avengers 2, so depends on the order of his next projects. If Captain America 3 comes out before Avengers 3 (rumor has it Cap 3 coming out in 2016 right after Ant-Man), then yes, I think there's a good chance we will loose our original Captain during Avengers 3.
Not to mention Winter Soldier has 8 more contracts after Captain America 2, the studio is so preparing him to be the next Captain.
One thing bothers me is that Captain America should be killed AFTER the great crossover event- Marvel's Civil War. However, since SONY/FOX has no intention to let the separated children (spidey/X-men) reuniting with the Marvel family, a civil war movie will not see daylight in any intimidate future. So they're going to kill off Cap (if they are indeed going to) in a very different way.