There have been other members that ran into the same thing with glow plugs breaking off and as I recall they can be drilled and sometimes removed with an Easy Out bit. I'm sure others who have been there done that will chime in with their experience and solution.
Regardless, don't give up! Its just testing you. Yes, when things go wrong it can be VERY FRUSTRATING!
When I get to that point I usually walk away for a while. After a couple of days or so I usually come back more determined than ever to win the battle with whatever I'm wrestling with and I usually succeed. Being tenacious and pushing through can be very rewarding and satisfying in the end.
Whenever any glitches/malfunctions/ailments present themselves I usually end up learning and understanding much more about my generators by enduring the frustration and pain. That knowledge learned through these events can come in real handy in the future!