It seems as if the manga is different than the anime. The second-to-last issue of the manga is out in America, and, at the end of it, Majin Buu has just absorbed Mystic Gohan. And the final issue most certainly will not have enough pages to cover all that happened in the anime after that. On the official website of the American company which does the manga, Viz (whcih does a good job; they do their anime uncut, so, I'm assuming their manga is, too), in the summary of the last issue, it ends with talking about who Goku will choose to fuse with. So, maybe, Vegitto will beat Majin Buu, but I'm not really sure. But it was weird, though, in this (actual original Japanese) Playstation 1 Dragon Ball Z video game (I can't remember what it was called; it was the only one of three Dragon Ball Z PS1 games with an actual story mode), the game ended after you beat Buu with Mystic Gohan. I'm not sure. I just can't wait to see what happens in the final manga.