Won't miss Cooper whilst sliding in Harris at 10? Seriously, even the people who hate Cooper realise how important Cooper is to the Reds and that the Reds are a much better team with Cooper at 10 than Harris.
Case in point is 2012, and the way the Reds struggled initially with Harris at 10. He couldn't get the backline working. The Reds looked best when anyone but Harris was there, but unfortunately they all went down injured. When Cooper returned, they won all three games with him at 10.
Harris is best at 12, maybe at 15 after his appearances there for the Wallabies. But for the Reds, he hasn't been too good at 10 so far, and I think Harris' game is a little too limited to play 10 for the Reds. With Tapuai surely occupying the 12 spot, Harris either gets 15 or a bench spot.
If Cooper is gone, I'd give Lucas first crack at 10 and hope that Lane signs as the back up. Lance and Harris would be fighting it out for the 3rd option.
Given how often Lucas has gotten injured in the past couple of seasons, whoever the 3rd choice is will get plenty of time anyway.
Even without Cooper, the Reds can still field a damn good backline with plenty of depth - Genia, Lucas, Ioane, Tapuai, A. Finger, Shipsanity and Harris/Morahan is still one of the best backlines in Aus with F'Sautia hopefully playing well enough to demand a starting spot soon too. Lance, Davies, Frisby are all more than handy squad players as well. I'd say that you could argue that only the Tahs' full strength backline would look better on paper (Hart/McKibbon, Foley, Mitchell, Horne/Carter/AAC (Adam Ashley-Cooper), AAC (Adam Ashley-Cooper)/Horne, Turner, Barnes), with the Rebels close.
The issue will be that Cooper was the magic that unlocked a lot of the Reds' attacking plays.