Recently in the sixth season of Arrow, it has been announced that Roy Harper will be returning this year. From what we saw in the trailer for that episode, Roy is being tortured by Ricardo Diaz and Anatoly Kynavez is involved in this
Roy chokes Thea

Roy is coming back!!! Yay!

matter. This will be a reason why Thea wants to suit up as Speedy again just to rescue her first love. I have a theory that Ricardo Diaz planned this whole earlier on before season 6 by tracking down the Arrow and discovering that it is Roy after learning from his people on his inside (A.R.G.U.S presumably) that Roy is still alive and that he was never the Arrow. He might have then tortured Roy for information causing Roy to break down and reveal Oliver's secret to him. I think Oliver will be understanding towards Roy. However, this would be repetitive of what Tobias Church did to Rene in order to make him talk.  I an article that I've read recently, people want Roy and Thea to have a happy ending together. However, I don't think it'll happen since Roy is a fugitive and since he will only be appearing for a few episodes with a small arc. Colton
Quentin Lance

Roy might harbor a grudge against for Quentin because of season three or Quentin might be feeling guilty about ruining Roy's life. This would be an interesting arc. I honestly don't know what's going to happen, but Quentin and Roy should interact again.

Haynes has other commitments as well, but you never know. There is also a part of me that feels that Roy should meet with Quentin Lance again. Remember in season 3 when Quentin ruined everything for Oliver for not telling him Sara died? I imagine Roy must hate Quentin for what has happened or Quentin has felt guilty about it. What probably would make Roy angrier is after he learned Quentin was in league with Damien Dark and he would probably blame him for Laurel's death. I don't know, but this could make Roy harbor a grudge against Quentin. It's not really Oliver's fault all of this happened in Star City. I have a feeling that if Oliver hadn't returned from Lian Yu, the Dark Archer would still be around and destroy most of the Glades, Ra's would attack Star City because of Malcolm
Eobard Thawne in his Harrison Wells wheelchair once again

Oliver returning or not, Eobard Thawne still would've created the Flash. Barry would've probably became consumed in all that rage when that meta did that to him in 'Flash V.S Arrow'.

violating league traditions, Adrian Chase becoming Vigilante since his father disowned him, Roy being dead, Barry would still become the Flash and face off against Thawne & the other metahumans, and among other things. I bet Quentin would hate Malcolm more than anything and consider him the one responsible for everything. Again, this is off topic.  I have a feeling that Roy could bring Team Arrow and the Outsiders (Rene, Curtis, and Dinah) back together again

I think Roy will solve all their problems. Then they would work together to help with Oliver and Rene's legal problems.

hopefully. He would tell the Outsiders what it was like working for Oliver as his accomplice and convince Team Arrow as well as the Outsiders to trust each other again. I bet he would also tell them why he chose to impersonate the Arrow in order to get Oliver out of trouble when Quentin was being out of control. That would actually be a good idea and I bet the whole gang can work together to make Watson look bad and get Watson to be unable to attack them legally. This would be something that Diaz, the mastermind behind the whole thing, didn't take into account. After all, he's not Clifford Devoe.