One Piece creator Eiichiro Oda doesn't kill off characters very often. Even rarer is him bringing a dead character back to life. Brooks is an exception, unable to die because of his specific devil fruit powers.
But Oda also enjoys creating scenarios that would be logically impossible, which suggests that anything is possible in the One Piece universe. That brings us to the question that fans often raise: Will Ace come back to life?
Can fans expect to see Ace again in One Piece?
The general consensus is no, Portgas D. Ace will not return to life in One Piece. Creator Oda has clearly stated that he has no plans to resurrect Ace anytime soon. However, there can be exceptions, as discussed below.
Son of the former Pirate King Gol D. Roger and Luffy's sworn brother, Ace was beloved by fans. But plot-wise, his primary function ends before the time skip in the 517th episode of One Piece, becoming the trigger for Luffy's growth.
Ace's presence in the story would cause some drastic changes, and while those changes would not necessarily be a bad thing, it isn't integral to the story. Moreover, Oda is known to dislike the idea of reviving dead characters from his childhood, when he read mangas where dead characters coming back to life was a trope much used by writers.
"Bringing a human back to life is something strange, isn't it? If a mangaka decides to revive (a character) who has died, then he shouldn't have to kill that character in the first place."
Finally, the series shows Ace's devil fruit, Mera mera no Mi, eaten by Luffy and his sworn brother, Sabo. If Ace is brought back to life, he would probably have to find a different devil fruit and hone those newly obtained abilities since he can no longer be "Fire-Fist" Ace.
Can characters in One Piece come back to life?
Oda has previously mentioned in an interview why One Piece characters do not come back from the dead. Besides the fact that he actively dislikes the trope, One Piece characters have a vitality few other animes have, surviving the most challenging situations.
So to bring back dead characters disregards the impact of those who managed to live through it all.
Even when a character who had been presumed dead comes back, it's mostly because they aren't actually dead. Sanji is an example of this, his father having faked his death causing Sanji to run away from the kingdom of Germa.
But to answer the question: in rare cases, even characters in One Piece can come back to life. Like 'edo tensei' in the Naruto series, Dr. Hogback and Moria can "resurrect" the dead. Still, it is only the lifeless corpses of dead people being possessed by stolen shadows.
The only character in One Piece to come back to life is Brook, the last surviving member of the Rumbar Pirates and now a part of the Straw Hat crew. He was revived thanks to the Yomi Yomi no Mi, but since each devil fruit is distinctive, it is unlikely that another such devil fruit would let them restore Ace.
One Piece fans should not lose hope, however. Lurking about on Reddit and Discord are theories about Marco's Tori Tori no Mi giving rise to Ace. While improbable, it is not an impossible scenario. For now, we can just wait to see what Oda has in store for us.