I've kinda been wondering this for awhile also. Over the last year or so and for a few years prior when MS first announced it's plan for WP7 and it's incompatibility with previous WM OS, I felt there was a serious flaw in their marketing and market plan. then to introduce an OS that wasn't really able to compete with what was already out there was another misstep.
I feel they lost a lot of people with this switch over to WP7 and have not tried very hard, until recently, to get them back or show others why they should have stayed. By this time, many, if not most, of the WM crowd have moved on to Droid and iOS. I cold have very well been one of them myself had I not had the opportunity to move over to WP7 for $35 as a service exchange for my TP2 by Sprint.
If Nokia continues to make trend setting phones like the Lumia and continues to advance technology and options then, even if WP doesn't make it in the market, they should be able to easily adapt their phones into the Droid market. I just don't know if they can meet the lower price points that many of the Droid phones sell for and still clear a substantial enough profit to carry on. They definitely build a device that's appealing and marketable. It's the poor marketing of the OS that's going to be the downfall, if it occurs.