The point is entirely different: if you update the channel-list you need the network for any changes to the configuration and I don't know of a way to go back to an earlier channel state.
`nix-channel` does have a `--rollback` flag to it.
However, I feel that Nix Flakes would allow you a better experience. With nix flakes, the revision of the nixpkgs input is persisted in a lockfile. You could check this file in somewhere, and then getting your working directory back to a known working state is much easier.
This is not a support forum and we're not trying to diagnose and fix someone's issue. It's just not that hard to get into trouble with NixOS and there's still a room for improvement, that's all.
Reading on `nix-channel --rollback`, it should definitely help in some cases and I don't know how I missed it, maybe the docs weren't clear it's not tied to config generations or I just didn't pay enough attention.
Unless you erase your darlings: https://grahamc.com/blog/erase-your-darlings