If the nipple is stuck in the cylinder you can drill it out. Start small and perfectly aligned and keep increasing the drill size. The nipple should collapse and come out just before you get into the cylinder threads. Of course you'll need a drill set with a lot of sizes so your increases will be small and a good vise to hold everything in alignment.
Did this myself with a GPH I bought used. Didn't even need to re-tap the threads, though I think I got lucky.
If the nipple is out but the threads are so bad you can't install a new one, you'll need someone who can drill out the threads and install a helicoil.
Doing nothing may be your best course. You're only supposed to load 5 anyway, so leave the chamber with the bad nipple empty.