Safely uninstalling GNOME desktop environment on Fedora 29

You can actually remove and install packages in the same operation, with dnf swap. And since the option takes groups as well as just single package names, you can switch one for another very simply:

dnf swap @gnome-desktop @kde-desktop

As the other answer point out, you can remove all of GNOME with # dnf group remove gnome-desktop. This will delete most of the packages even not related to GNOME itself (Xorg for example).

However if you just want to switch from one DE without complete reinstall, you can install other environment with e.g. # dnf groupinstall kde-desktop. This will bring back X and all the nessesary packages as in fresh Fedora spin.

One annoying little thing I found is that you have to reinstall packages like chromium using dnf. They will keep their configs though, so it wasn't a huge deal for me.