https://www.githubstatus.com/history lists 72 incidents since January
Perhaps this is a continuing argument for self-hosting, especially if you don't have to expose the instance publicly. But then, if that's an option, you can also self-host GitHub (though I have heard less anecdotes about the stability of that).
I'm confused. You can do zero-downtime backups and replication of databases. I don't know what your company / Gitlab are doing but it seems wrong.