But since Nokia has much more at stake in the partnership (unfortunately for Stephen Elop) than Microsoft, for which the mobile market is but one line of business, Redmond conceivably could lose interest in the deal.
But with a market cap of $224 billion, Microsoft could easily absorb RIM. It would save on WP7 development costs, plus it already has a strong presence in the corporate market, where RIM has excelled (though that's also eroding). Maybe Microsoft could craft a two-tiered mobile strategy, selling higher-priced BlackBerrys along with cheaper WP7s.
It sounds a little less crazy today.