The instructions say if we finish the game It'll all go away

The end of Jumanji, with young Alan and Sarah and old Alan (Robin Williams) and Sarah, did it represent separate timelines?
Presumably the game has been played numerous times and only a handful of people ever remember it, because they have eventually finished the game and changed the world back to how it was before. And probably due to experiences never want to play it again or really talk about it, for the better. So that's why the game gets dumped/ buried/ thrown into the sea and is rediscovered while people simultaneously have no idea what Jumanji is and are intrigued by it, like Alan was at the beginning.

At the end of Jumanji, it was as if the events of the movie never happened. Alan never disappeared into the game. Think about it as time travel if you want. Bad things happened, they beat the game, went back before bad things happened and go to relive their lives again.

They went back to their original "timeline" as the game was finished. Nothing else that happened matters.

But what are the ethical implications of winning the game for Alan? Sure, the devolved madman's ultimate fantasy comes true for him, he is made young again and gets to date the girl he liked. But at what cost? The two other children featured throughout the movie are erased from existence. It doesn't matter that they sort of come back at the end with no memory (because their lives are different). Think of it like this: Two people existed, and then the entire universe resets 20 or so years previous and now those two people don't exist. They died. Those children died. All so Alan could get his way, he sacrificed the lives of two innocent children to the mystical evil board game.

What happens to the other timeline? Does it just continue?
It would be a bit disturbing if it did. It's not Source Code, it's Jumanji- magic, just doesn't explain. Source Code had such a copout ending it should have ended with the kiss. That would have been the more artistic ending, but it also would have left things unresolved. It's been a while since I watched it but I remember it not making any sense and coming off as just happy tacked-on. It's also actually quite dark when you think about it.

Anyway, Alan had been taken into the game, so he lost years of his life inside it, and that had to go away. The only way to do that is to reverse time to that night before he started playing, so obviously everyone who was affect by his disappearance would forget. They remember because they had been the only two to start the game at the beginning so they were the only ones who remember. When the game finishes everybody goes back to the day they first played it, and only the players remember that they played it at all. Notice how depressed Judy was? Judy and Peter were miserable and hated what had already happened in their short lives. Alan saved their parent's lives in the rectified timeline, allowing the children to keep their beloved parents.