The people who will first have access to sufficient quantum computing power (to hack bitcoin) will be the entities that created it, e.g. university research departments, government labs, major technology corporations, etc. These people will likely not use the technology for nefarious purposes, and they will have access to the technology long before the bad actors will.

So let's say the US government is the first major entity to have access to advanced quantum computing power 20 years from now.
By that time the US government could  be sitting on hundreds of thousands of bitcoin in their strategic reserve, that was originally started by the Trump administration.

It would be in the best interest of the US govt. to protect the value of its bitcoin reserves. One way the US govt. could do this is to be the first to "hack" Satoshi's original stash,
not to seize it or steal it but in order to move it safely to the new quantum resistant bitcoin wallet(s) that would exist in the future.

Or perhaps the bitcoin devs could simply create a new protocol to invalidate or permanently lock up ancient wallet addresses that were made under the original less secure system of addressing,
which would not effect the more secure SHA-256 wallet addresses in use today. Just an idea, don't know if that could actually work or not.