My point is that in the event of a catastrophic cryptographic failure, the network could be temporarily halted, a quantum-proof blockchain could be rebuilt using hash1 as proof of ownership.

Here's how I would do it. First I'm assuming the existence of an asymmetric cryptographic scheme that is quantum resistant.

You cannot just reveal hash1, because once hash1 is public the attacker could use that knowledge to claim your coins as well.

1-on the legacy blockchain, you own 10 coins in an address called address_legacy. No coins from address_legacy have ever been spent, so your coins are safe.

2-start a new blockchain with addresses that use an asymmetric cryptographic scheme that is quantum resistant

3-on the new blockchain: generate a new address called address_new

4-on the new blockchain: issue a special transaction saying "I claim the 10 coins stored in address_legacy". Here's the trick: to prevent an attacker from doing the same this special transaction would require a high fee, and the privilege of claiming the coins would be limited in time ( let's say 2 hours). During that time, only address_new would be able to claim the legacy coins. So if an attacker wanted to claim your coins, he'd have to pay the fee every 2 hours quickly exhausting his resources.

5-issue a special transaction on the new blockchain revealing hash1, proving that you own the coins on the legacy blockchain. The network will then credit 10 coins on address_new. And your vulnerable public key on the legacy chain is still secret.