What state do you mean? Let’s say you have a backup of your system partition but your home folder is separate. In that case a rollback with the filesystem is the same as one through nix — the latter will place symlinks to all the previous versions and the finished result is identical.

Of course if you have in the meanwhile used the new system and your home folder contains some backwards incompatible changes, both solutions will fail. Rolling back your home folder may not be a good thing as you may have backwards compatible changes you prefer.

Also, nix can also manage installed application’s configs, so those could also be rolled back, on either a per-app basis or however you prefer.