Why would we need to save what's on there? Just wipe it clean with the usual tools and backup again. Many fine reasons to refresh that file system!
If we are talking data recovery (you admit this is not a backup copy?) then we clone the drive and operate on the clone. This way we can try tools and commands over and over.
http://windowsitpro.com/systems-management/fix-unbootable-systems-bootsect notes the force bootsect command.
I accidentally disconnected a backup HDD while my PC was running and have destroyed the MBR or something! I know it is possible to restore it because I did that for someone years ago but I've forgotten how it goes. Does anyone know - it can't be done in Command Prompt as far as I can see,