Deepbit just hit 50%. We are still alive. Now everyone stop whining.
This proves you DON'T GET IT. It's not a "50%..the end" thing...its a
User A: "....some time later...what's this? double-spending? can't be...."
User B: "@twitter...btc chain broken..sell."
Thing.
The possibility of your scenario is so slight that it's not even funny.
In the even that it did happen, the price will drop, mining won't be profitable and everyone that's only in it for the money and they would get out.
The network would recover and rebuild, a little more wiser.
From a new block chain. Thats not a very easy thing to do, now that people can look at the original Bitcoin blockchain and say "Oh, yea, you can double spend in that thing.... Not very secure. Lets NOT use that technology."