TL;DR
If you still have all three seeds (and the passphrase), you can rebuild the descriptor. If you’ve lost the descriptor and a seed, you can’t recover unless you find a copy, so search everywhere before you do anything else.
Why the descriptor matters
Your multisig addresses are calculated from all three public keys together. The descriptor holds those three keys plus the rules: 2-of-3, the address type and the derivation paths. Two seeds give you two keys. Without the descriptor you’re missing the third public key, and without it you can’t calculate your addresses. More on this in what is a wallet descriptor.
Descriptor lost, all three seeds still there
You can rebuild it. In Sparrow, create a new multisig wallet with exactly the original settings and import the three devices:
- File → New Wallet, Multi Signature, 2 of 3, Native SegWit (P2WSH).
- Unlock each device with the passphrase if you use one. Without it you get different keys.
- Import each device with the same derivation path as before, normally
m/48'/0'/0'/2'. - Check that the first receive address matches an address you used before. If it does, you’ve rebuilt the wallet.
- Export the new descriptor straight away and store copies as in step 7.
Descriptor lost and a seed lost
This is the situation multisig can’t save you from on its own. Before you assume the worst, look everywhere a copy might be:
- Every box with a seed backup: the printed PDF and the USB stick.
- Your password manager, email, cloud storage, old computers.
- Old wallet files from Sparrow or another wallet app, including on a laptop you replaced.
If a copy turns up, rebuild the wallet from it and move your coins to a fresh multisig with a proper descriptor backup.
Preventing it
The descriptor holds no private keys, so copies can’t be used to steal. Keep one in every box with a seed backup and a few digital copies. They cost next to nothing.