Interesting story, but I'd hardly call this "sacrificing his fortune." The title led me to believe that perhaps there was some sort of looming intellectual property or non-compete battle -- instead, he just spent his money in development efforts for his next game. That said, the game looks great -- and I'm sure he'll be very successful with this one, too.
Yes, this could be more accurately described as "investing his fortune", or if you want to focus more on the risk (as game development is a risky business), "bet his fortune." Loved Braid, quite interested in trying out The Witness; hope it doesn't take too long to come to a platform I can play it on, as I have neither a Windows machine, nor any consoles, nor an iOS device.
I guess people see him as "winning the lottery" with Braid, so now spending that "lottery money" is seen as a foolish move. However I think that spending/investing your hard-earned money in something you enjoy (developing games) is the best investment one can do, even if you do lose all your money.