There is simply no way Akainu can be alive by the end of One Piece. He is far too stubborn and extremist too accept Luffy and his allies win and see them rebuild and transform the whole World including the Marines. He would rather die than let Luffy ruin his Absolute Justice ideology. In addition to that he killed Ace right in front of Luffy which makes it even more likely that he will pay the ultimate price in the end.
So Oda will need to find a way to get rid of Akainu. Permanently. There are different options to do so. Luffy and Sabo have a strong reason to kill him. Dragon is the guy Akainu hates the most besides Luffy so there is a good chance for Dragon vs Akainu here.
Then you have Imu/Gorosei and Blackbeard who in typical villain fashion could take advantage when Akainu already got beat up by Luffy and then kill him. Blackbeard to just get rid of a strong character and an opponent. And Imu/Gorosei because they expect Akainu and loyal people to him in the Marines to plan a coup against WG.
There are probably even more options but I don't want the list too be too long so there is the "other" option. And obviously the "Akainu won't die" option when you think that Oda will find another way to get rid of him.
So Oda will need to find a way to get rid of Akainu. Permanently. There are different options to do so. Luffy and Sabo have a strong reason to kill him. Dragon is the guy Akainu hates the most besides Luffy so there is a good chance for Dragon vs Akainu here.
Then you have Imu/Gorosei and Blackbeard who in typical villain fashion could take advantage when Akainu already got beat up by Luffy and then kill him. Blackbeard to just get rid of a strong character and an opponent. And Imu/Gorosei because they expect Akainu and loyal people to him in the Marines to plan a coup against WG.
There are probably even more options but I don't want the list too be too long so there is the "other" option. And obviously the "Akainu won't die" option when you think that Oda will find another way to get rid of him.