If you stored your xpubs with each seed and you lost 1, couldn’t you just configure a new Multisig and with the 2 private keys, send btc to your newly configured wallet? It’s rather annoying, but no loss of funds.
Discussion
The multisig address is a hash of all 3 extended public keys.
If you don’t have these, you can’t recreate the wallet.
If you lost one seed phrase, but had all 3 XPUBs you would be able to recreate the wallet.
I follow you there. At that point you still have access to your funds. Maybe I’m misunderstanding, but you configure an entirely new multi sig Wallet with 3 new xpubs, yeah? I see your point, you no longer can recover your wallet which is annoying for several reasons. However, no loss of funds from losing any of the 3 xpubs is my understanding. I certainly could be wrong or misunderstanding the situation.