can "File system check exit code is 8" be repaired?
Generally speaking it depends on what you mean by repaired.

That error indicates that the filesystem on that disk is damaged. The good news is that if you reformat it the disk will still be usable. That is also bad news, as you may have noted.

You can try running disk utility on that drive a few times (3 - 4) and see if is repairable. Depending on the filesystem in use on the drive you may be able to use something like DiskWarrior to fix the disk. But beware that DiskWarrior and pretty much all disk repair utilities can't repair APFS volumes (yet).

If that is the case you can try a data recovery utility or sending the drive off to be recovered for you, which can be expensive.