Given Nokia's position Elop's job is very much at risk. Should Elop be fired, the directors will be bringing in someone with a new plan. One which deemphasises the use of WP. This would be a disaster for MS already low market share in the phone arena.
Another aspect is that should Elop get fired, for the first time in history "Someone will have been fired for using Microsoft." A fact that could potentially reverberate very badly in other areas of MS.
For these two reasons, there is severe pressure on MS to acquire Nokia before Elop gets fired.
There is however another aspect to this deal. WIth Nokia's large portfolio, it is very likely that both Apple and Google will complain to antitrust authorities in the EU and the EU anitrust people have not been kind to MS.