Greed is what stops people to withdraw the winning amount and they keep playing thinking that the next bet also they will win and get more profits. But in gambling we do know that win is only temporary and in long run people will lose their money. So better to stay away or else if win take your money and leave.
Well being able to savor the feeling of winning gives you a belief that you're invincible so probably he's not going to stop since its a pretty big amount that he got. Best advise would be just to practice caution since we can't really tell him to stop
I don't think so the amount what he won is so big but winning is always a profit so it is better to book some profit and continue gambling again with a smaller amount. Otherwise, if he loses back those winnings then can't say that won so much money in few minutes. Gambling always temps us to continue playing so we should know when to stop it for our advantages.