Having been my own boss most of my life, I cannot imagine being hostage to any of my employees, ie., I would not in my wildest dreams expect any employee to know more about my business than I do. If he did, I'd be paying him a healthy bit of compensation
So, tell your employer that both he and the new cnc machinist should work together and come up to speed on running the machine. That way, the calibre of jobs being undertaken will have to be within the combined skill set of both persons:
"Do you know how to do it?"
"Nope, how about you?"
"No clue, let's check the Haas manual"
Blame and success can be jointly shared.
There are certain basic jobs that can be accomplished without too much delay, I suppose, but new guys need a chance to grow in experience to accomplish more challenging work.