Quote from DesertTrader:
These things tend to trade for years on the OTC market. Look at LEHMQ.
When you exercise your long put, someone is assigned and you have an obligation to deliver the stock to the individual/account. Thus you are short the security unless you purchased it before exercise. The OCC is not the counterparty; however, they guaranty the transaction in case of default.
If you are a retail trader and endup short GMGMQ, they may force you to cover since the stock is a penny stock. Depends on your broker. If a large number of other positions are exercised at the same time (option expiration) you may be forced to cover in competition with others in a thin market.
I would hold the position as long as possible since the odds are that GMGMQ drifts to a nickel or so in time. Just before exercise, buy the stock in the OTC.