Only if they're not backing up their phone, which seems insane in this day and age.

And even if they're not, if they have a computer or tablet, the passkey will still be available there assuming they share an account.

You can also recover your iCloud Keychain via a designated/trusted Recovery Contact (e.g. spouse, who presumably hasn't destroyed their phone at the exact same time), or via iCloud Keychain escrow.

https://support.apple.com/guide/iphone/passwords-devices-iph...