Not much of a fan of IM2, I always felt BW didn't belong in it. The entire film was a letdown from the first IM.
The more I've watched IM2 the more I liked it, but I still think it's weighted down too much by setting up The Avengers and I think it handled Tony's alcoholism way to lightly and the "party scene" was just absurd.
Black Widow comes off as another character who needs someone to play off of. She doesn't strike me as big enough or interesting enough to have her own movie. They would have to give her movie something special to make it work.
I think a Black Widow movie could very well work but it would be much more of spy or Jason Bourne movie than a grand superhero movie. An "origin story" with her on the wrong side of the law being hunted down by Hawkeye would probably be the neatest way to go, and bring Hawkeye into the movie and give him some much needed development.
And I seriously doubt the sequel is going to pretend that he never made it back to Earth. He'll simply explain to Jane that it was an emergency situation and there wasn't time to say hi (which she should understand, if she had any access to a TV at the time).
Well, I doubt that too. I just suspected The Avengers would have dealt with Thor's return to Earth and then his own second movie would deal with him returning to Jane and his protection of Earth. In fact, would have expected Jane to have played a hand in Thor's return.
Along those lines, in Thor's movie he destroys the Bifrost in order to save Jotunheim. Loki implies that he'll never see Jane again and later when Thor talks to Heimdall he asks if Earth is lost to them. Can they not rebuild the Bifrost? Or would the reconstruction of it last longer than Jane's lifetime?