One of the main themes of One Piece has always been “inherited will”, and for those of you who have seen those popular theories, will understand how strong that argument is.
The greatest symbol of this concept is the famous “straw hat”, which was passed down from Gol D. Roger to Shanks and finally to Luffy.
Luffy’s goal of being Pirate King is also tied to proving to Shanks that he will be a great person, and returning the hat to him once that is accomplished.
I believe this scene of returning the hat will be one of the final scenes of One Piece. However, I don’t think Shanks will be there for that picture. Shanks is hands down one of the most powerful characters currently in the world of One Piece, but there are a couple of reasons why he won’t be around for the end.
1- The story of One Piece heavily focuses on the older generation making way for the generations of the future. This can be seen with the Supernovas making names for themselves, trying to take out the Yonko and very possibly taking their positions. And also with the Navy, where the old generation of Garp and Sengoku have stepped aside letting the next generation of Admirals proceed onwards. Due to this focus, it is very likely Shanks will not be a Yonko while Luffy is Pirate King.
2- Shanks is TOO powerful to be an ally to Luffy in the grand scheme of things. If Luffy faces adversity like at Marineford, there is always that chance that Shanks can show up and save the day. That does not seem like something Oda would want for his protagonist who is trying to be the King of the Pirates.
3- Luffy is currently not strong enough to be the Pirate King and needs another push to get more powerful. The initial push was not being strong enough to save his brother Ace, which propelled Luffy to who he is now. However, his current strength is not enough to take on Yonkos. With the death of Shanks to a rival like Blackbeard, Luffy gains even more hatred of Blackbeard and the kick he needs to get even more powerful. Shanks has already shown how dangerous he believes Blackbeard to be, and the mark on his face is proof of that.
Based on these three reasons, it is highly likely that Shanks will be dead before Luffy gets a chance to give the hat back. There are people that believe that Luffy would return the hat at a funeral for Shanks, but I believe something else. This come back to the themes of inherited will and moving from generation to generation. Luffy was motivated to be who he is by being around Shanks; Shanks eventually became a Yonko after originally being a rookie pirate under the former Pirate King; and something has to continue this going forward for the next generation.
I believe that once the secret of One Piece is revealed, Luffy became Pirate King and the Straw Hat Pirates’ journey will be over; the Straw Hats will separate and return to their individual homes. Waiting for Luffy back in Foosha Village is Makino and her child. This child will look up to Luffy, and Luffy will take interest in him too. The most famous theory out there is that the child is Shanks’ and Makino’s son mainly because Oda answered someone’s question in the SBS by saying that Makino’s child is “probably that person”.
I can see things going this way: Luffy will notice the resemblance of the child with Shanks and remember his promise to his former idol. He will pass on the Straw Hat to this child and pass on his will to the future generations. Assuming that this child is also Shank’s son, Luffy will be able to keep his promise to a certain degree. It’s a heartfelt moment that provides much needed closure. But most of all it leaves that open ended finish for imaginations to go wild about future generations in the amazing world that we all spent years reading/watching.
*Theory by UrsaKing