In my perspective, I don't see many big changes happening. So instead of just saying who needs to leave, I'll try to address the big needs on the roster.
1. Size
It's been known the whole season that we're lacking a PF. Can PWill be that guy in the future? Who knows, but even if the answer is yes there is still a need for size on this team. Pretty much the whole rotation stands between 6'5 and 6'7 with Vuc and Thompson being the only bigs. And Thompson is only 6'9. With Simonovic likely still a couple years away from being any meaningful rotation player (if he gets there at all), there's pretty much no bigs on the roster in 2 years time and only Vuc, Simonovic, and Tony Bradley (player option apparently) are under contract for next season. Given BD's reluctance to actually use Tony Bradley at all, there's room for up to 3 rotational bigs on the roster, depending on how you feel about PWill.
FA pickings are slim to say the least. Among PFs listed on spotrac, potentially helpful options include Robert Covington, Chris Boucher (likely to re-sign with Toronto), Bobby Portis (likely to stay with Milwaukee), Trey Lyles (team option), and Montrezl Harrell. Among Cs there's not much either, but some options include Demarcus Cousins, Mitchell Robinson (likely re-signing with NY), Andre Drummond, Hassan Whiteside, and Javale McGee.
2. Shooting
It's well documented that the Bulls are near the bottom of the league in 3PA, but for much of the season were near the top in 3pt%. Some of that is the Derozan effect, but this team could certainly use more consistent shooting from 3 with volume. Without Lonzo's 42% shooting from 3, we have been left to see Coby White's streaky performances and Alex Caruso's shooting woes due recovering from a plethora of injuries simultaneously, as well as Ayo's inconsistency as our primary 3pt shooters outside of Zach. Even if we were to say that Caruso will return to 40% shooting form as he had with the Lakers last season, he is still only attempting 3 attempts per game.
While Matt Thomas is a good shooter, clearly he has many weaknesses that keep him off the court. Potential shooters that could crack the rotation and are FAs this offseason include Malik Monk, Bryn Forbes, Robert Covington, TJ Warren, and an intriguing option in Victor Oladipo.
There is also the potential to hire shooting coaches. Chris Matthews, aka Lethal Shooter, has worked with many NBA players with great success including Bobby Portis, public enemy #1 Grayson Allen, Danny Green, and Kentavious Calwell-Pope. Portis in particular has experienced significant improvement since working with Lethal Shooter. Were I a part of the Bulls FO, I'd look into getting some players to work with this guy, or at the very least get some more consistency out of players you know will be shooting the ball. Someone like Javonte Green's value could skyrocket with a consistent corner 3.
3. Defense
This one I am going to pin more on the coaching staff than anyone else. I can't claim to know in full what BD's scheme is, but it has gotten progressively worse every single month. Whatever it is, it needs some revamping. You don't need elite defenders across your roster to have an elite defense. There's so many breakdowns that happen now that seemed to not happen earlier in the year. Maybe players were more engaged earlier in the season when there was more winning, but regardless of what it is, the scheme needs to be better and adjustments need to happen quicker. How long does it take to realize that double teaming so and so has led to 5 open shots for someone else?
At the end of the day, I think the only real changes we'll see is in the role players. I don't see Vuc going anywhere, despite the many clamoring for his departure. Coby I can see being moved for a PF not previously mentioned, but don't expect any game changers anywhere. However, hopefully with some of the holes being filled and the right types of players in the rotation we can go from a 1st round sweep expectation to a solid 2nd round appearance.