I would like to make a few points , This is only possible because your dad is the only one who has to deal with this program and also he only works on this one big complex thing which he knows really well .
oh hell yeah, absolutely. This sort of code is not uncommon at all but is pretty much incomprehensible (let alone maintainable) for anyone beyond the original implementer
If one day somebody else does inherit the codebase, are there any tools out there that are designed to help people in that situation? Like something that de-spaghettifies everything?
Some automatic tools could help (although I doubt thay'll work on DBase III): Static analysis to see what's there, version control to start at the top and log your way through and be able to rollback to a previous working version.
