I am new to option learning.
I have this question.
I hear this thing that almost everybody sells their option position before expiry. So if everyone sells their position before expiry then who is the last person who buys options?
Last person who buys, buys it from last person who sells 
Buyer needs a seller, seller needs a buyer - kind of obvious, isn’t it?
I feel his query is the last person who buys why would he buy for the limited number of days remaining in the option.
The way i understand is the last person buying gets the full number of days and not limited to the remaining days of the original option
I feel this was his query not sure. Hope he clarifies
He would have sold it earlier and now wants to take a new position. So he has to get his margin released first.
Thats the reason you see options trading at 0.05 and 0.1 even at 3.29PM on the expiry day. Otherwise why would he even want to forgo that amount and also pay brokerage. Its all about cost benefit. If he sees higher benefit somewhere else be will close his existing position.
And there are traders who like to buy on expiry day. Previous expiry, the day started with Nifty more than 3 % away from a strike and in the first hour it was worth around 1 Rs - later the velocity of fall was immense and the first time Nifty fell past -2% around 2pm, the premium on it went above Rs 8. It eventually went back to 0 as the fall didn’t sustain and the strike expired otm.
There are instances when some have made 50 times. Expiry day option buyers can make a killing with 10-20% success rate. Its like a lottery ticket.