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.
Both you and outhue pointed out that the fix would be implemented right away - and I too think there should be no panic behind such developments because it's natural to think about things that - may - do something.
But in the end, BTC would endure, without a little breach or not. And that is what matters.