The only way the series will end in the next 150 chapters (5-6 years) is if Oda decides to do it with battle royal style and throw all the Emperors and the Navy into battle at once to get the OP.
As long as we continue to follow the SHs from island to island, meet countless new characters, numerous flashbacks etc etc, the story will continue until he dies.
There's no way he could wrap up the series with all these stuff left in less than 10 years without completely screwing it up.