This is the fair question to ask a small studio, so here is the plain answer. There is no second person on standby. What there is instead is the thing that actually matters: from the day a project ships, the repository, the credentials, the deployment steps and the documentation are in your accounts, not ours. The site does not depend on us being reachable to stay online, and any competent developer can pick it up without a conversation with us first.
For work in progress, the same applies to whatever is finished at that point. You are never in a position where the only copy of your project is on somebody else's laptop.