How do I fix this?

Guys, help me save my Miata! I was driving on the 405 and I heard a loud bang. I pulled over and noticed that my spark plug wire was popping out. I got out, tightened the plug and the car ran smooth. Next day, it happened again however I couldn't tighten the spark plug back to the valve. I disconnected the fuel injector to that cylinder and drove home. The car was extremely unsafe but I managed to make it home. The threads are stripped so I can't put a new spark plug in. What are my options? Is this fixable?