self hosted won't insulate you from your VCS instance failing.
I used to work at a medium-sized company with Gitlab 8 years ago, it was running into several issues and required frequent maintenance.
The best example to learn from is ReactOS who while has moved to GitHub they at least have a self-hosted backup just in case GitHub falls over. [1]
For the ones who are not on GitHub and are self-hosting (OpenBSD, Mozilla, Linux Kernel Project, GNOME, xfce, wireguard) I don't hear any complaints from them.