I don't foresee Microsoft giving up on the smart phone wars. Windows mobile may be down, but I don't think it's out. They just need to try something different.
That said - why not consider Windows mobile development? If your going to start new and try a new language; may as well try one where there is minimal competition.
For a while, I was actually a huge fan of Windows mobile. The problem is and always was, a lack of good apps for it. Had good apps been available, I'd have switched (from using an iPhone from day 1 release)