Are u saying that it was never happend because no one every said that?I missed the chapter that said this.
OT:
1.Sadly Ace is dead.
2.He was buried along with WB by WB & Red Hair Pirates so it is not possible for him to be alive since we are talking about OP not Naruto.
3.There is no proof to say that Sabo is dead and only thing that we know for sure is that he was attacked by C.Dragon.
4.Dragon saved someone at that time and that man was assmed to be Sabo.
5.Luffy don't know the location of Ace's grave and he never visited it so only remaining one who knows about Sake cups is Sabo.
6.A man from revolutionary army appeared at Dressrosa and Luffy has an unknown relation with him.
7.Luffy thought that he was dead.
With this many good reasons,any OP fan with a little brain can say that it is Sabo and He is alive.