If you have the Xpub of the 10 co-signer then you can use it to recover the other co-signers without having the need for the 10th seed phrase since you wouldn't be needing it for signing of the transaction. you can simply just create another multi sig again and move the funds there because losing of the sedd could have reduce the security of the wallet.

if someone gets hold of one of the co-signer details then with the ratio of n:m used, they might be needing just one more co-signers details. except if the xpub and derivation path isn't on the lost back up