I mean people already answered your question, but I want to know why you want to leave kde plasma? It was the best I have found (after gnome, but in gnome I can't change shit)
Do you mean files on your computer or open on the kde desktop? If they are open and you cannot save them for some reason and wanna jump to another DE you can do that by starting another x-server on a new vt, then you can jump to it with the ctrl+alt+F#-keys. I don't remember the commands to do this, though.