In the end, the only thing that keeps Microsoft going is the fact that it can depend on US law to prevent 'unauthorized' copying. Furthermore, US law is what allows the BSA and other groups to go after people creating unauthorized copies.
There are other accounting things that may bring them down, like floats keeping their stock heading higher and higher and valuations of the stock options.

It may, if due diligence is done, be the accountants that bring them down. Of course, Microsoft can afford to buy off accountants faster than they can find things (as they seemingly have). Hell, I have a business major degree, I'll work as an accountant for a year or two if it would give me a paltry million or two.