Microsoft is gigantic, rich and relentless, they do not give up. Look at the amounts of cash they've been burning on Bing for years patiently waiting for their opening. You should not never count them out.
I'm not counting on Microsoft giving up on its products - I just see them as patiently burning through cash (generated from its successful cash cows) without making a significant splash in mobile. Just because they can afford to throw away money doesn't mean that they'll be successful at all of their new ventures.
This isn't exclusively a Microsoft thing either. Look at Google and its multiple attempts at new products (Wave, Buzz, Google+). They can obviously afford it because of their own cash cow, search.