Re: (Speculation) Captain America III: Fallen Son (The Death of Captain America)?
Figuring Cap 3 likely will come before Avengers 3, my answer to this is ZERO chance of happening. Evans will be in Avengers 3. Captain America will still be Steve Rogers. Also, I would MUCH rather see Rogers as Cap (and see a recasting) rather than Bucky take over.
But, I don't think this has any chance of happening. Unless they kill him in Avengers 3 (that has a chance of happening, but then again, anyone can die in Avengers 3).