How about the trade deadline passing as well? Trades can't happen on 2008-09 contracts anymore (never mind that has already been said that Marbury has a minimum contract). Marbury is a free agent.
There is also that issue of the Cs roster salary being about $100M (before lux tax) if you plop Rip and Prince on top of what they already have signed next year and after they fill out the rest of the roster. They are not spending that kind of money.
Now whether either side would do Ray for Rip and Prince is a whole different story. That's at least plausible although very unlikely.
I think the Pistons want to stay somwhat competitive even while angling for 2010, and really even with Prince signed for 2010-11 they have an enormous amount of cap room. They would actually have more flexibility in some ways, as it is unlikely that 2-3 top free agents will all be signed by the Pistons in the summer of 2010, even if they have $40M in cap room. Prince would be another avenue to getting players to surround whoever they may convince to sign as he would certainly be a good player to keep, but he would also be a nice large expiring contract as well to move. In fact Dumars may do a few two year deals this year to entice some of the better lower cost free agents (guys who may only be getting one year offers from other teams), so he can both build a solid enough team this year, but remain very flexible for next year as well with expiring deals.