Doubt about ITM options

As we all know, option prices go to zero on expiry. So when Profit or loss is calculated, will the ITM options PnL will be calculated from zero or LTP. For example if 30000 PE which is Deep ITM expires at LTP 800 rs, the trader who has sold it at 1200 will get 400 Rs or entire 1200 rs.
Kindly excuse if you find this silly.:pleading_face:

The trader who has sold it at Rs 1200 will get a profit of Rs.400, because it is in the money. Only OTM options expire worthless (Zero).

Since the option expired ITM it still holds value so trader who shorted it at 1200 will get 400, for a trader to get full 1200 option needs to expire OTM.