I read Roy Harper/Arsenal might make appearances in either The Flash or the upcoming team up spin off. Ray/Atom gave both Felicity/Oliver and Roy's car quite the look. I expect he will be on his way out soon and we will see him on the spin off too.
I also checked to see if Willa Holland is leaving too but there was no news of that. I assume Oliver will take Ra's place to put her in the Lazarus pit.