You can always track down the original template on the web, download it, and re-install it manually (the same way you would install a template that was not in the "one-click" bundle).
You might also investigate the .snapshot directories to see if an "unborked" copy of your template is available there.
This would put your template back into the "original" state, and not effect your "one-click" at all.
In the future, you might find that copying the template and working with a copy can be a lifesaver (just rename the original template directory something like "orig_templatename"); then. if you screw it up, you can just delete the borked one and rename the original to it's original name.