i would be worried more about the chances of bitcoin to survive, before the quantum pc will ever hit the market on a large scale
it doesn't need to hit the market on large scale...
right now bitcoin with its silly marketcap would not be a primarily target of hidden quantum computer, other big targets would be in the list before bitcoin
That depends who has the first quantum PC, and who has connections to avoid the big theft.
Like if some big bank funded research makes the PC, they wont be hacked, but their rivals could be.