Is a new found exploit going to kill Bitcoin? Possibly.
Yet, in 2010 somebody was able to find a bug good enough to produce 184 BILLION BITCOINS for themselves. Did Bitcoin die? No, a solution was found and the problem was eventually solved.
This is what I expect will happen to Bitcoin in the event of a Quantum Computer powerful enough to 'kill Bitcoin'. A solution will be found and we will simply move on after a few minutes, hours or days of panic. That is it.
i'm not too worried about bitcoin dying because of an exploit or even a quantum computer. It sounds scary at first but bitcoin has already survived some pretty big issues.
if a quantum computer ever becomes a real threat i believe the same thing will happen. People will find a fix and we'll adapt. It happened before and im confident it'll happen again