When I worked in systems engineering, some of the folks a decade or two older had supported tape-based computing systems. Tape damage happened all the time. They would splice it back together, manually repair corrupt bits and bytes with something like a hex editor, etc. I don't know all of the details, but IIRC sometimes they'd use magnetic viewing film, which you can still buy.

It might not be documented well online, but if that really is the last copy in existence, it would be worth tracking down some mainframe-era sysadmins to ask for tape recovery advice, IMO.