FWIW it won't fall into the combustion chamber but into the prechamber.

When 606 glow plugs break apart during removal the part that doesn't come loose usually stays in the glow plug threads and has to be extracted like a broken bolt. I've never heard of a glow plug breaking apart during removal in a way that some part comes completely loose in the prechamber. The prechamber would have to be fouled beyond all functionality before there's enough crud to impair removal of the glow plug. Or am I an optimist?

Sixto
95 S420
87 300SDL