What happens to ITM stock options on upon expiry

What happens to stock option price which goes deep ITM upon expiry day?
for example suppose I buy Reliance PE of 930 @ 10 . now reliance expirary day spot price is 900. What will happen to my PE if i dont exercise?

You will get 20*lotsize at end of day

Be sure to square off all ITM options before market close on expiry day other wise yu our position may turn into loss due to hefty STT…

Isn’t that fixed?