You think Marion has played his last game as a Heat?
Doubtful, all these phantomish vague injuries have been coming up probably because the Heat want to tank. They probably told him 'listen, the East is weak, and will be next year. Lets just rest you this year, we'll get a great draft pick, and next year the core of Marion-Wade-Haslem-#1 pick will be able to make it into the playoffs no problem."
If Marion really wanted to opt out and try to get a big deal next year, he'd be doing everything he could to stay on the court this year and put up huge numbers and drive up his value. I've said all along that I don't think Marion will opt out, he's just not worth more than what he's making. So unless some idiot GM gives him a ridiculous deal (which I suppose is within the realm of possibility), he'll be on the Heat next year.
Ricky Davis and Jason Williams are both unrestricted Free agents, I don't have a clue what they'll do with them. On the one hand, they are super thin up front, so maybe they'd go after a free agent. On the other, the 2008 NBA Free Agent class is horrible. Depending on where they land in the lottery, Brooke Lopez could be a good pick for them, since they have decent wing talent and serviceable PGs (Quinn/Banks).