True. But, it has been hinted that the focus will shift to the others. And, they have been saying that season 4 will be a bit on the lighter side. Thea seems to be gearing up to take on the red hood and jacket. New villain will be tied in with H.I.V.E..
Currently, Amell is off filming different projects, so, leaves little time to film any Arrow episodes. At least for the first half of the season. I get the feeling that he will only return in a supporting capacity from time to time. Even if he returns as Green Arrow, people will still know it is Oliver Queen. If green arrows start popping up in the city, the police will know. Unless they do a time reversal or something to wipe out that knowledge.