If MSFT were to buy RIMM, I seriously doubt MSFT would do anything drastic to RIMM. its strategies and products in the short term, because RIMM would simply be a money generating vehicle for MSFT, there is just too much different between WinMo and BB. At best MSFT would put its logo on the BBs, but the BBs will still be the BBs, with a MSFT logo of course. This is no longer the "If you can't beat it, buy it and kill it" era anymore. MSFT is not stupid, it knows how much RIMM is worth.
This case also applies to NOK or others want to buy RIMM, therefore I do not foresee any drastic changes to RIMM's product offering, regardless who buys RIMM.
Just my two cents.