On a shared wallet, if one of the recipients deleted their wallets off their phone, is there a way to rejoin?
Any money sent to a 2-of-2 multisignature address will be forever inacessible if one of the private keys is deleted (e.g. by uninstalling the phone app that holds them) and no backup was made and no recovery phrase was recorded.

There's a common aphorism that circulates in the bitcoin world in various forms, sometimes described as Bitcoin Rule 0


No private keys -- no Bitcoin
Not your private keys -- not your Bitcoin


The latter refers to web-wallets where the wallet-provider business holds the private-keys and their customers do not, or where an online "friend" creates a watch-only wallet for you. The first form of the aphorism is apt here.


One fifth of Bitcoin is permanently lost