I think that it has one last roll of the dice. Look at Microsoft as a whole and whilst it does have some exposure in the consumer space it is predominately an Enterprise business. If it is to be a success then it should embrace the Enterprise market for mobile solutions and buy BlackBerry. In doing so it would have an operating system capable of interfacing with Exchange Servers and open up a wide range of poosibilities for itself and its partners. A BlackBerry that is part of Microsoft would be able to move into the Blue Collar sector and stop losing Professional customers thanks to imporoved Channel Partners who could deliver customers in the tens of thousands.
In the early days of Mobile Data Windows CE was used in the majority of handheld terminals used in logistics, field service engineering and government sectors. As mobile has become more important to businesses Microsoft has lost its focus and whilst some have attempted to eat into the market with the launching of Apps. These Apps are a compromise given that iOS and Android do not have enough APIs to open up all the functionality needed for Enterprise Mobility.
The rise of Apple and Android has lowered the valuation of BlackBerry and Microsoft has a large cash pile that it can use to fund a purchase. BlackBerry can be happy with a new owner that is unlikely to closedown it's Canadian offices and make large redundancies rather they will have someone likely to invest and increase the workforce so Regulatory approval will be easier than say selling to a Far East Manufacturer or Software company.