This really is very similar to what happened to Sony Ericsson. They had Symbian and UIQ with more or less full control over UIQ at least. But UIQ reached a dead end (and at that point, so did Symbian as well), and eventually SE reached a point where they had to simply stop throwing money out the door. Thanks to Android they are still alive - for now.

Nokia could also go the Android route, but chose to go Windows Mobile. In the long run this will be better than Android, if they succeed. How bad it is going to be for Nokia until it becomes better, is entirely a result of how well they handle Symbian the next couple of years, but I guess MS has promised to step in with cash as well?

In the end, I don't think Nokia had much Choice. It was either Android or WP. Lucky for Nokia, MS was in a tight spot as well, so they had some leverage in the negotiations.

We should also remember that what Nokia and MS are saying now, is not necessarily what is going to happen. I still find it hard to believe that Nokia will let Symbian die just like that, and my bet is that we will see Symbian devices for a long time some way or the other.