Microsoft, however, have three products that will ensure their continued profitability - Excel, Exchange and (probably most importantly), Active Directory. This is over and above their insanely cohesive ecosystem, from SCCM all the way to Dynamics.
Active Directory is so critical because of the vast amount of legacy code that depends on it. Want to guess how many fortune 500 companies rely on AD?
 Nothing is guaranteed so yes, unless they evolve as the environment they generate value for inevitably evolves, they'll go.
Fast forward to 2013 ... what do you see? Did Ballmer really improve Microsoft position in enterprise comparing to Oracle and other competitors?
Every sizable company already has these things installed. Smaller and new companies may choose to spend their dollars elsewhere and that's a change of events for Microsoft. Projects that previously would go on Sharepoint are now done less expensively with cloud services, for example.
In tech, growth is in consumer, and with consumer tech drifting in to the enterprise, even enterprise IT spending may not go to Microsoft.