I hinted at this a couple of weeks ago, but have committed to not comment on mental health, physical health or other private matters of players. They tried very hard to give him enough time to recover without surgery and play this season, but that was apparently not going to happen. it started to become more and more apparent over the last two weeks, but they wanted to play it out. Ultimately, he still can't push off of the foot, even after extended rest.
I disagree with you a bit on the notion that "Estrella was already struggling to find major minutes". That definitely was not true pre-injury. In mid Summer, he was getting minutes at 4 to 1 over Cade. Post injury he wasn't getting practice or game minutes because he couldn't stay on the court due to pain (that may be what you meant). A healthy Estrella would be playing meaningful minutes and contributing to the team at a serious clip. His offense in June/July was vastly improved over last year, and he obviously has a much higher ceiling than Cade. Prior to the season, I mentioned that Cade would play quite a bit more than Carr and would deliver on effort, rebounds and defense. At that point, people in the program told me that Estrella was a 75% chance of not recovering fully without surgery. I think it was a bit of a fantasy that they thought he could just play through a fracture, but it is what it is.
I think losing Estrella is a material loss, but not insurmountable. Wooden used to say his biggest fear was a short roster, and that injuries are "contagious". He meant that when your key guys are playing over capacity, more injuries come. I don't think that's the case here, but it is a risk. I agree with you that a mid-season add that will be a core contributor is very unlikely. Right now, I do think there is a chance that there is a mid-season addition, but that it is merely to get to healthy practice numbers. This is unlikely, but possible.
Finally, I mentioned (before Dubar took a break for personal issues) that he had three back to back internal scrimmages with the ones, scoring 12+ in each outing. I am not going to comment on why he took a break, or how he overcame it, but he can be a serious contributor. If you like what he's doing now, give him time to work back into team chemistry and flow. He's a tweener, and an odd fit in this offense, but he can score, rebound and defend. He can also drive and pass well. I think he will give us some solid minutes. To me, the key to this team is the addition of Igor and Lanier as a more balanced scoring contribution than what we had last year. I don't think teams can focus on shutting down the outside without giving up the inside. ZZ and Mashack are guys we'll remember for decades, but they always needed scoring support. I hope we can bring back Carr and get Bishop into the lineup, and avoid injuries. This is a quality group that is balanced enough to be a top four team in the conference and a 1-3 seed in March.