Undo just reenters the entries that RegVac removed.
Another option is the Registry Backup and Registry Restore in RegVac. Restoring a Registry Backup will put the registry back to the place it was when the backup was made.
Sometimes the Undo does not work because other software has made changes in the registry but restoring a Registry Backup made before RegVac was run will always correct what RegVac did.
Restore Points in System Restore sometimes have registry backups in them and sometimes don't. The problem with Restore Points is that they usually have more than the registry backup in them and restoring a Restore Point may change more than you want to change. WinRescue does have the ability to restore just the registry backup in the Restore Point.
So if you want to undo the changes that RegVac makes, I would recommend using Undo first. If that does not solve the problem, restore a RegVac Registry Backup made before you ran RegVac. If you do not have a RegVac Registry Backup, try restoring a Restore Point.