What Should Stay Recoverable When a Vendor Leaves?

A vendor can be dependable today and still become unavailable later. Keeping a full duplicate of everything in-house may be wasteful; keeping too little knowledge can make a transition painfully expensive.

Before making an external service critical, what would you want the team to retain or verify internally—a named owner, a usable data-export path, recovery instructions, or a tested alternative? And how do you keep that evidence current without turning an exit plan into paperwork nobody uses?