A) No, Baron would not do it. He lives a pretty expensive lifestyle here in the Bay Area and is also seriously pursuing the media production business he's starting, which tells me he is going to want to secure his final long term, large contract this offseason.
B) If Baron was available for the MLE, and Posey had signed elsewhere, I really don't see why they would not jump at the chance. It would possibly hurt Rondo's confidence and progress, and Baron might not be the best fit for the Celtics, but he is a great point guard, so why not?
C) Absolutely not. You don't bench Ray Allen for a guy that is one of the highest volume/low percentage 3 point shooters in the game. Baron is a point guard, you would bench Rondo.