There's a lot to be said for trying to snap out of this and go back to normal, and then only change one piece of himself at a time, because Keltham does not have already set up any other ways to be.
It would definitely sound like the sort of standard advice that a Watcher would give you about what to do if you've had an overly large epiphany.
Keltham continues to sit and think, for a time.