gihun had no idea anything about ali's family to give them closure. they went back to pakistan so it would have been very difficult to track them down since they were apparently in korea illegally in the first place.
also to me it did make sense for sangwoo to give up. he had already been planning to kill himself before they went back to the game and the fact that gihun refused to take the win over him made him sacrifice himself when he couldnt fight anymore AND didn't want to go back to the real world.
gihun clearly did not give ALL of the money to sangwoo's mom... that one suitcase was not full of 40billion whatever won lol
also, sangwoo's mom knew he was on the run from the police. its a pretty easy assumption to make that she has accepted he prob took his own life. or ran away. she has no idea gihun was involved with what happened to him. or maybe gihun gave her an explanation off screen.
gihun also obviously told her the kid was an orphan and she took him in. old people take in orphans irl too.