But looking back on it, I would say out of my current perspective this Mel guy was not a genius, but one of the worst programmers you could probably hire:
He written unmaintainable and even unchangeable "write-once" code that was so complex that nobody else could handle it either. He refused to do what he was payed for and just went away as he lost interest.
One of this kind of dudes on your engineering team and your company is in real deep trouble…
It's a given that you will need to throw away everything they did and start form scratch should any changes be necessary later on. However there's one fundamental constant in software engineering: Your software is going to need to change over time! No mater whatever somebody told you upfront. So in case you've got software built by some "Mel" you're completely screwed at that point, especially as changes to SW are usually needed the most at some critical period in time for your company.