Like sys said, two players are transferring and two have questions surrounding their ability to qualify.
Paul has all but confirmed that he's gone. Stone is the other one on the way out, as well. What I've heard is that Paul wanted to leave at the semester but was convinced to finish the season. He wants to go somewhere that will give him a chance at more PT. He will end up at a BCS conference school.
I don't know much about Stone's situation, other than he was simply recruited over. He'll be looking for something that will give him an opportunity to play, I'm sure.
Everyone around Mizzou seems very confident that Mitchell will qualify. He took the ACT for the first time today (don't know why he waited so long), and what I've heard suggests all he needs to do is pass that. I know there are people (some here) who believe his transcript is going to be a major hurdle, but I haven't heard that at all from the Mizzou end.
Green apparently is much more likely to not make it. Like Mitchell, he's been to several schools... but he also has the added hurdle of starting off in Canada. Bad grades at multiple schools in multiple countries can't make things easy.
Paul left completely on his own and has wanted to leave for awhile. He posted something on his facebook today (that he's since taken down) about how he'll consider himself a Tiger for life, how he loved everything about it, but he needs to do what is best for him and his family and find somewhere that will let him play more. He definitely was not pushed out the door.
Stone, I'm not so sure about. I think it is a case of a mutual understanding that he just isn't ever going to be a factor here. He has the physical potential/skills, but not the mentality.
The Stone situation may be similar to what has gone on at OSU... but that's one guy, not several.
Edit: Also, for what it's worth, both players transferring were present during Ratliffe's and Pressey's visit and helped recruit these two players to take their spots. If they were pushed out without being willing to leave, they probably wouldn't have played an active role in recruiting their replacements.