Robert Morse
Sponsor
You are contractually obligated to follow the OCC rules and your contract. If you are long calls and ITM, you must buy the stock at the strike price. If short, you must sell the stock at the strike price. If you are not long stock when your short calls are assigned, you are short stock. Your clearing broker will try and make good delivery by the settlement date. If they can't borrow the shares, at some point under Reg-SHO rules they will buy back your short.
What if a call expires in the money and you don't have the shares to deliver?