Unless Star City is somehow transported to another reality, the show may not be able to find a way to remove Oliver and Arrow from the Arrow-verse without killing him off.
The poor guy deserves the chance to retire, but Arrow doesn’t seem to like to give him breaks without throwing tragedy at him shortly thereafter.
Of course, there is still one major problem with Arrow ending after Season 5, and it has everything to do with the rest of The CW’s DC universe.
Oliver can’t really be lifted out of the equation very easily, especially considering that Arrow is directly responsible for setting up both The Flash and Legends of Tomorrow.