Originally Posted by H.U.S.T.L.E.
It seems that you're assuming that Cap 3 will return everyone (Cap, BW, Bucky, Falcon) from TWS by that statement. Who's to say that Cap 3 will feature all of them again? It's certainly possible, but there's been no indication that the Cap franchise has to include BW for future installments. And since there will be an Avengers movie in between, that may have ramifications for Cap's supporting cast as well.
I just don't think it's a given to assume that it's going to feature all the same players. And really, that's the beauty of this shared universe... we've already seen BW in Iron Man 2, so there's nothing that explicitly ties her to Cap's franchise.
Nothing is a given, but it is likely.
Natasha was in IM2, but she didn't integrate into the franchise much.
From everything we've heard about this movie, Natasha has been Steve's partner for two years, and is now his best friend. Given how they'll continue to work together in AoU, and the potential for a connection to the Winter Soldier, its doubtless she's coming back.
Bucky and Sam are Steve's best friends in comics, and I doubt they'll return one and introduce the other just to kill them off within the next movie.
Really, the only reason any of them won't return is if they get their own spinoff out of the blue. Or if one of the actors is arrested for smuggling seven kilos of heroin.