I've had a sparkplug cross thread before, my grandpa who must of had this happen before, took the old sparkplug and chapmpfered the threads with a grinder to turn it into a tap. Ran it in cleaning up the threads and then removed and installed the new sparkplug. It's a no/low cost solution, if you still have the material there for the threads to grab.
I’ve never done a head before but I’ve tapped into places where the metal shavings couldn’t remain. Having a small nozzle of a shop vac held by a helper to pull out the shavings. Go slow. You are gambling of course. In my experiences it was a safe bet. In your case pulling the head might not be much work