"Its impossible to change back to simplicity once you change away from it."

Impossible? I think not. If you can't get to LSTS or LSCP then just open the ...\litestep\step.rc file and change the paths to a theme that does work (simplicity). Check taskmanager for a running instance of LS and close it. Then just run litestep.exe and you've successfully changed themes.

Edit: Sorry, Mr Goat. Sarcasm is difficult to spot when it's written :)