If you don’t square-off your MIS position before cut-off time, RMS will square-off it off, if the markets are volatile or if there isn’t any liquidity as you mentioned above then even RMS will not be able to.
In the scenario where you or even RMS isn’t able to square-off your position, depending on moneyness of the Option your position will expire either Out of the Money or In The Money and depending on this any profit or loss you make will be credited to / debited from your account.
Also, if you are Long and your position expires ITM, there will be additional STT of 0.125% charged on Intrinsic Value of the Option.
If it is not expiry day and your MIS position is not squared-off, either by you or by RMS, then it will be carried forward to the next day under NRML product type.
If it is long position, you have already paid entire premium upfront so there will not be any change, for Short positions margin will be according to NRML product type.
There are no additional charges. however as mentioned above if you have long position and if it expires ITM, there will be additional STT charged at 0.125% on Intrinsic Value of the Option.