Why trade a 23 year old defensive stud who has grown his offensive game year after year? You're gonna have to play a second big with Mobley most likely, anyway. Mobley and Allen can both switch and guard the smaller players, I dont understand why you think playing them together wont work long-term?
Now, they need shooting around them in the worst way. I know they've been trying, but Id continue to try and flip Sexton for that. Garland is near 40% and improving, just needs to take more. Ice needs to get better from behind the Arc (~35% this year would be awesome). Sexton needs to get a little better if they keep him, but mostly needs to shoot the 3 more. Hes a walking bucket, but the shots he takes for the most part are losing shots. Mix in about 6-7 threes a game and that would be a drastic improvment over the 4.4 this year.