Solo dev here, with a mobile app that has paying subscribers. The part that worries me most is not the server but the app store accounts. Apple and Google developer accounts are tied to me personally, so even if the right people get the message, I'm not sure they could take over. Did anyone here solve the store account side?
Add your 2IC as an Admin on Apple (you need a organisation account) and with Google Play console invite them. You can keep a master document, put the 2FA recovery steps in it, and keep that master password separate from the document. Happy to work through any issues with you mate. :))