if you ever used your wallet it leaves an unhashed copy of your public key out there on the network for anyone to have - a quantum computer of 1556 or more qubits can take that public key and reverse engineer out your private key.
how fast will this quantum computer be able to factorize the public key into it's private key? it has to be faster than a miner can mine transactions transferring to a quantum resistant keypair.
also, don't forget that miners will want to continue to mine, so if a new keypair scheme is available, one can simply send (encrypted) transactions directly to a miner, transferring utxos to a new address using the new scheme.
what's that you say, the quantum resistant keypairs don't exist? well neither does IBM's 4000 qubit computer.
did you say game over?