When that happens, game quality will drop through the floor. It costs millions to make a AAA title today. Noboddy is going to invest that kind of money on a platform that doesn't guarantee a good return or that offers a far smaller return than an alternative platform. PC will become the domain of small, independant devlopers working on a limited budget. Doesn't mean that there won't be some gems. But mostly it will be the B-movies of the gaming world.
You can still make lots of money in a niche market. PC gaming is not going to die it will just become smaller than the console market.
You just have to look at sales in europe to see the pc gaming market is still very strong.
I don't see B movies happening to pc gaming.
Also the modding is very important part.