I think you get wrong what "existance" means, Chara isn't able to destroy all of reality, Chara is able to destroy all of the games timelines, that's for sure, however, after Chara destroyed the timelines, the space-time still existed, we know this because Chara was able to make the True Reset, if the Space-Time didn't exist anymore, they wouldn't be able to do it since the True Reset since what it does is recreates the timelines that were destroyed, with the lack of time, that wouldn't be possible, Chara is mulit-universal 4D because of that fact.