In the interests of being productive, here is what I would do now if I were in Underwood's shoes:
1. See if Ebo and Matic are willing to entertain coming back. That may be unrealistic, but it's worth a shot. He should want both guys to return and be willing to address their concerns from their first year here.
2. If you can't get one or both of those guys back, hit whatever is left of the grad transfer market and find at least one big man who can soak up 10 minutes without getting annihilated on defense or fouling out. Two would be better still. It's totally unrealistic to expect Kane and Giorgi to give us much of anything as raw, fringe-y true freshmen who aren't even native English speakers.
3. Call Erik Pastrana, Underwood's assistant at SFA now at Florida Atlantic, and Stephen Gentry, also an SFA assistant who was our DOBO before leaving for the same position at Gonzaga, to see if they would be willing to join as an assistant. Failing them see if there is anyone else who is familiar with our offensive style in particular with experience who would be willing to take the job at this late juncture. If so, let go of Jamall Walker tomorrow. We need Chin to keep Ayo, Antigua has the big man coaching challenge of his life ahead of him, Walker's clearly the chair you open if you have to open one, and we really really do to get someone with a background in UnderwoodBall.
4. Reach out to both Kipper and AJ and gauge their comfort and willingness to totally redefine themselves as a full-time starting 4. Pick one of them (AJ is a guy who will do anything for the team so he'd put his heart and soul into it, but if Kipper is eager for it he probably has the more natural skillset for the role), and assign them all of the nutrition, weight training, and one-on-one coaching they can handle to make that transition. Rather than juggle nine million guys playing out of position, sacrifice one to the cause full-time.
5. Retaining as much terminology, base concepts, base skills and whatnot as possible, ease up on the pressure D for the time being. Do pre-emptively what OSU did on the fly during his year there. We just don't have the personnel for it physically or experience-wise, and it would be demoralizing for all these young kids to just get posterized over and over again.
6. Get your team together and level with them. As the coach, it's your job to make a balanced roster, and you've failed. You've put them in a bad position, and put them in a spot where they're going to face a lot of havoc and make a lot of mistakes. You coach hard, you're not going to change the way you coach, but you also understand that you have not put the pieces together in a way that can make everything fit the way it does in your head. Create some sort of a pathway outside of regular practice and meeting times where each player can discuss the way they're being coached and their concerns. Nurture those lines of communication. Make clear that if they're willing to work for you and willing to stick with you that they have not just a scholarship but a playing role on the team for the duration of that scholarship.
Then you have to go coach and recruit your behind off of course. But that's just my short-term idea to stop the bleeding.