I'm haivng the same problem as realx. I deleted my character settings files and quest helper is still gone. Tried replacing the window with default quest helper window, and other quest helper windows to no avail.
EDIT: realx, I fixed mine, what I did was re-download, and re-install the UI. Re-installing from what I already had downloaded did not fix it.
Also, you might have to delete the character files again.