First of all, via the template editor you should not be able to change anything in the templates that are shipped with Limesurvey. This should only work with copies of these templates.
If you made your modifications via an editor directly into the files of these templates, then there is little we can do. You could just download LS again, unzip the folder, go to the file and copy it into your installation via FTP. This should work.
What version of LS are you using?
We're going into production and this needs to be resolved ASAP!
Well, I only can recommend not to do those things right before going into production, without having a backup at least.