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.
But if I am long an option that expires itm I am not contractually obligated to do anything. The problem is the broker may have a rule that any contract that ends .01 itm will be exercised unless instructed otherwise. So if you are long a call that finishes $2 itm, instead of cash settling the position for $200, the broker will exercise the option and purchase 100 shares of xyz, and put your account in a margin call? Yes you could sell the shares in the morning to clear it up and take your profits...but what if the price dumps pre-market? It seems the broker is taking on unnecessary risk for themselves and their clients if they handle it this way.
That is the OCC rule- .01 itm and will generate a Reg sho violation. They tag you when they become repetitive and you broker. Especially problematic - if you're US. This is one where you want to talk to the Firm's 24 compliance directly