You people seem to forget Bethesda is owed by ZeniMax. Bethesda's fragile egos don't factor into this story, they don't have the option to lock it up in their vaults.
ZM uses Bethesda as a cash cow, they would not be happy if the cash cow runs dry. Somehow Bethesda convinced ZeniMax Fallout was the license to go to and while one could argue it wasn't a good pick ZM went with it.
But if Fallout 3 fails, ZM would be all ears to a good offer.
Thing is there's nobody looking to buy, with the kind of money they'd want.