I liked Tommy and I'm glad CD comes back occasionally but I don't want him back for 10 eps of S8, though I wouldn't be surprised at all if he does pop up for one or two.
I thought Tommy's role in S1 was to show how they really weren't best friends anymore, they'd grown apart in the 5 years (obviously). Oliver put on the playboy front with him and Tommy hated Oliver the murderer/vigilante etc. Then the Laurel issue.... If he'd stayed on the show that would have lead to him taking up his father's mantle rather than Malcolm surviving being stabbed through the heart. He could have done it after TommyX.
I do like him and would rather see him and Oliver than with Dinah or Other Dinah but then that probably pushes Dig out and he's been Oliver's brother and Yoda since the beginning.
I'm not really that big a fan of fan fiction Tommy, he often comes off as a bit too perfect, mature and can do no wrong to Oliver's fuck up personality to me.
CD has been between series before and hasn't been brought back full time or for more than one episode so it's not necessarily guaranteed here.