If it is proven the Microsoft has put in one or more backdoors on purpose then the ramifications for Microsoft are much larger than rebates.
Can anyone with a need for a secure system accept the possibility that Microsoft has illicit access to their systems regardless of what they may have done themselves to secure it? Governments, multinational corporations and competitors would pretty much have to say no to Windows with any online connections of any sort. The lawsuits that would result would make the antitrust trials look like a mild cold versus the plague.
Wholesale migration to alternate systems would be pretty much an automatic result.