Genetic Chaos forces you to randomly mutate. Without Robust Genetics, chances for disadvantageous mutations are significantly more likely, and Deterioration downgrades into Disintegration. These mutations cause pain and damage at regular intervals, eventually resulting in taking more damage than you regenerate and, ultimately, a gooey death.
http://cddawiki.chezzo.com/cdda_wiki/index.php?title=Disintegration
Thing is, with Genetic Chaos and Deterioration, he’s already on the Chimera path. My advice is to either cram him with as much purifier as you can make, or as much mutagen as you can make and hope he mutates away the Deterioration, although with GC it’s only a matter of time before it comes back. He might melt into goo by mutating or (unlikely) become the luckiest bastard alive and mutate into a nigh-unstoppable combat monster.
