I didnt read any of the posts, so sorry if this has been pointed out already. Lets say for argument sake that Elop would leave Nokia to become CEO of MS. Lets say Elop would be the main pusher of WP strategy at Nokia (the board holds the ultimate power in the company), and Nokia would be starting to ditch WP or take Android also..... With 80% of WP devices sold being Nokia made, MS would only have one option, they would buy Nokia's devices. Its been discussed in many places and its unavoidable. This is the only option MS would have. I dont think it needs to be debated, unless someone has inside information from MS that they plan to be the world biggest microwave manufacturer in 5 years, and they dont need to be involved in the mobile industry.
EDIT: What I think is not talked about much about Nokia's move to WP, is the fact that if Nokia would have been going to Android. Google would have done everything to kill Nokia Maps and who knows what services. Android was not an option to Nokia anymore, that late in the game. Earlier maybe yes, when Nokia had more power to demand things...