Fred won't be fired so I won't even entertain that. I don't think he's the right guy and it was a terrible move hiring him without interviewing other candidates, but unfortunately we're going to be stuck with him for at least a few more years, despite his obvious lack of leadership skills and coaching demeanor. Here's what I would do:
Let Pau and Noah walk. My goals for the off-season would be to get younger, more athletic, and get longer and tougher in the front court. I see this as a full rebuild and would treat it as such.
Re-visit the Butler to Celtics deal. If they still want to give up a top 5 pick, Crowder, and Johnson, I'm in. Chances aren't good for Simmons but I'd settle for Buddy Hield
Don't go crazy in free agency. Harrison Barnes, Horford, and Batum aren't going to be worth the contracts they get or put us any closer to a championship. Hold off for the 2017 class which is insanely loaded and deep.
Sign Bismack Biyombo to a modest 3 yr/33-35 mil dollar deal. That will be peanuts with the new CBA. Gives us a tough presence with length to go along with Bobby. Still only 23 years old.
Look to trade Niko, Snell, and MDJ for whatever. Niko will be due for a deal the following season and I wouldn't give it to him. Not unless he drastically improves his defense and keeps having games like last night. Neither will happen.
Rose/Moore/2nd round pick
Hield/Holliday/Moore
Crowder/Dougie
Bobby/Taj/Johnson
Bismack/1st round pick/Bobby
Hopefully come away with something decent for Niko, Snell, and MDJ. I'd take a 1st or future 1st.
In 2017 Rose, Taj, and Johnson all come off the books. If you haven't checked out that free agent class, I would suggest doing so. I wouldn't expect to land any of the 1st tier guys, but there's a TON of interesting 2nd and 3rd tier options available.