If I can't recover my original .wyp file -- and it's starting to look that way -- is there any way I can recover my original signing key, or, failing that, force the update to run anyway?
No. If you lost the original keys you can't reproduce them from nothing. For all practical purposes it's impossible. If you *could* reproduce the keys from nothing, then so could a malicious third party, thus negating the whole reason for update signing in the first place.
So your options are:
- Try to find a backup of the *.wyp file.
- Or, have the end-users manually re-install your app with a new client.wyc file, or have them manually replace that single client.wyc file (with the new signing keys, obviously).