How loyal would the customer base be if Blackberry switched to Windows Phone? Would they be any more loyal than Symbian users when Nokia did the transition?
This is why I mention only the patents. Those are clearly valuable. The customer base is debatable.
If Blackberry goes into liquidation the customer base breaks more or less like the market and WP get's .1% market share. Otherwise if they buy BB and can hang onto half of those customers. That would almost double WP's market share. Those customers are worth more to also ran WP than anyone else.
I'm just guessing that MS would probably want to digest one phone manufacturer before immediately buying another. Integrating one team is more than hard enough.