Unless the experience is inferior or somehow limited, google (and allies) will not let it happen. I think for a VAST majority of Nokia customers, it's the brand that matters. They buy NOKIAs. They don't look for 'Symbian' handsets, and most of them have probably not heard of Symbian before. So if Nokia takes up MS' offer (and I'm sure there IS one on the table right now), they can just sell them as Nokia smartphones (Now powered by WP7!) and the Nokia sheeps (yeah) will buy it.