Loosen the lid so the excess CO2 can escape and let that mason jar beer ride. You no longer can get the OG but you might get some interesting yeast out of this. When it is done fermenting (couple of weeks) take a sip of it. If you like it, use this like a starter for a new batch. If it is not drinkable, pour it out and think of what you learned. Then buy 2 new hydrometers so when one breaks...you have another one to break too.