The ur didact ( Shadow-of-Sundered-Star) was made to understand a gravemind, the human equivalent would probably be PTSD.
You cant even do simple tasks without your PTSD taking over. Imagine just going to fill up a glass, then smashing the glass then deliberately cutting yourself with the glass.
Also who would follow him? his warrior servants owe more allegiance to the iso didact, the builders are pretty much extinct, and the life workers are smart enough not to follow him.
The only Forerunners left in the galaxy would be, the monitors, Promethean knights, and perhaps catalog.