I guess 3rd brother is gone for good ..
https://www.kuaikanmanhua.com/web/topic/709/
Okay I think you're confused, he did go in the future, but that was time travel the same way gujiu did and she went to the past, but it doesn't mean she was existed in the past. The same way, third brother went to the future when twin gujiu and her sister were little kids, but now they're young so time goes on, and if third brother will die it doesn't mean he can't die cuz he went to future, as he went when they were children, and now they're young.
but if im not mistaken, the third brother show up in the future right? and he met shasha (gujiu sister) when she was little? then it means he’s not dead or what? i really confused now (⊙…⊙ )