I think he meant that in 4 months, they've had to pay out 3 billion. If the track record continues, they'd be paying out 12 billion/year. Over 4 years, that would amount to 48 billion.
The problem with this math is it doesn't take into consideration the money they will make off of Longhorn, Office programs, and whatever they make as the delve into the search engine arena. Not to mention their various other business ventures to get MS products into daily lives. It also assumes MS will lose money over the next 4 years, or at least maintain the status quo. Somehow I don't see this hapening...if they've done nothing else, they've shown their ability to make money.
I think it's overly optomistic to expect MS to go bankrupt. But if this continues, we could definately see some of the competition catch up.