If it is a real threat, yes it’s all tradeoffs. But if it’s not a real threat, then “upgrades” should be considered as an attack on the protocol. You can use Bitcoin to verify the ontology of time and verify the assumptions about a quantum threat. Bitcoin resolves through thermologic computation in time. In doing so, it reveals a new category of system in which energy, logic, and memory converge to produce the smallest observable unit of causal change. There is no second best quantum computer. No need to change the code.