Your broker, DTC and FINRA all have an obligation to make sure your shares are real and their value is supported. The way it is supposed to work is that when short positions become unsupportable (as in uplisting or a huge development by the company) there will be margin calls and forced buy ins just as their are margin calls and forced sales when a stock tanks.
I did do a quick check and could not find who OptionsExpress uses for a clearing agent. If it's Penson I would move my account to TDA or Etrade or another broker that self clears.
That being said, if the entire financial system blows up there is no way of knowing what will happen. If it does blow up I expect Penson to be where it all starts.
News 
Market Data 
Discover 
AI
