Positive impacts Gi-hun has had in other people's lives which will still matter even if the games get back on track, Gi-hun dies, and the games end with the expected sole surviving player taking home the entire ₩ 45.6 billion once again in S3:
Cheol is being raised by a financially stable parental figure who loves him.
Sangwoo's mother gets to focus on being a good parent to Cheol instead of drowning alone in her confusion, grief, and lack of closure around Sangwoo's disappearance.
Cheol's mother still has a decent chance of being brought across the border and reunited with her son, who is being raised in a kind and stable home environment in the meantime.
Saebyeok's broker is making a genuine effort to be a kinder/better person to all of his clients.
Junho and Wooseok know about the games and still have access to whatever remains of Gihun's winnings from the first games. Either or both of them could easily decide to continue carrying on Gihun's mission of destroying the games, even if Gihun dies.
The recruiter is still dead. (Less obvious, perhaps, on the 'positive impact' front, but it seems likely that he was one of the better recruiters the games had, which means replacing him will probably require at least some stressful/annoying work on the part of the game runners. They'll have to hope they can find someone else as well suited to the conman's job. If they can't, it might also become more difficult to fill all 456 spots with willing victims every year in future games.)
Gihun can't undo the selfish choices he made in the past or the losses he's suffered in the games, but neither can the games unwrite every act of kindness he's committed since.
Sometimes things feel hopeless because we get too focused on too narrow a view of our personal impact on the world. A win is still a win, though - an act of selfless kindness that helped someone else still matters - even when the bigger battles are lost, our greatest goals are not realized, and despair feels so easy to lose ourselves in.
There may always be cruel and selfish people in the world, but there will always be kind and caring people, too. The games can strip away hope and compassion from the people they grind down and destroy, but they can't strip all the kindness, all the people who choose caring for each other over selfish greed, or all the acts of selfless compassion that change someone else's life for the better from every person in the world.
Gihun can't stop cruelty from existing in the world, but the games can't stop kindness from existing in the world, too.
