I agree that you should take a step back and think this over carefully, first. This is what I would do:
1- If you haven't altered the external drive since the files were deleted, there are tools (some free) to undelete your files. When you delete a file, it's not actually deleted until you overwrite the drive with more data. I would attempt this first, given that the files are already gone and this won't affect your Zune at all.
Here's one tool I've used, that might help:
Restoration Freeware download and review - file undelete utility from SnapFiles
2- If you can't undelete the files, then the Zune is your last resort. I would NOT attach the Zune to your PC unless you are absolutely sure that auto-sync is not enabled. An even better idea is to use another PC entirely as you mentioned, and make sure that you setup the Zune as a guest (which automatically disables auto-sync). You will need to install the Zune Software first.
Even if you get this to reverse sync, keep in mind it could take a very long time to complete. Good luck.