Well we are safe for now from them.
This is why we have altcoins, obviously.
We don't really even need altcoins to handle this. Just plug in another private key encryption method into the client, one that's resistant to quantum computing, whenever it looks like QCs start to become a viable threat, and have everyone migrate to the newer addresses (or not, their choice.)
I meant altcoins for the supply. If bitcoins don't have enough supply we have altcoins for that.