I really don't understand the angst and animosity regarding HD perhaps not coming back to play. Talk about his "stealing" and "cheating" UK, and Cal messing up in this case seems way off.
What exactly did UK lose by letting HD practice?
Did it hurt recruiting other OADs? On the contrary it gives (as someone said above) another reason for parents and players to see Cal as "players first."
Did it cause team division in the locker room? No, but if he had gotten to play it very well could have been a dividing point; given that he would have taken minutes from someone, whether it was Briscoe who came back as a Sophomore and had put in 1 1/2 years or Hawkins who was finally allowed to contribute after putting in nearly four years of work (or Fox - who was the best player on the team).
Did he walk away mid-season next year taking game and starting five practice time away from someone? No (if he leaves now) he is really more like a "missed recruiting target," a guy you didn't get. Except he wasn't even that bad, since you didn't miss on him and have him show up in a Duke or Kansas uniform. Having him in Lexington for a semester insured we would never wear the colors of an opponent.
As for those saying if Cal thought there was anyway he might not be coming back he should have been playing him this past season. Well, that is just silly.
First off, he wasn't not playing him because it would have cost HD a year of eligibility. There was never any way he was a four year guy, so giving up a year meant nothing. So it wasn't future eligibility which was keeping him out.
On the other hand playing him could have caused huge in-team division. Imagine if when Fox was not playing well at Vandy that Cal would have inserted HD in the second half. And then Diallo would have made a late TO and (as new freshman are prone to do) hung his head and let a game turning dunk ensue. That could have been a disaster.
But more than that, there was no chance he was playing (unless Fox would have had a severe injury ending his season). He wasn't ready to contribute. The toughest things for freshman (IMO) are conditioning, understanding team offensive concepts (i.e. getting over AAU) and learning to play defense as a part of a unit. Those things all take more time and playing time than HD was going to get. That development happening with time is why Cal's teams are so much better in March than in December. (And why coaches love those off-shore games when allowed in September, and for kids to show up in June). HD was going to be able to help in practice with individual defense on Fox, but in a game he would have been schooled by other teams and out of position on D, and not ready for the full contact of games with adult men (aka juniors and seniors) that it takes months for the guys to get accustomed to, and he would not have been in shape to play hard for even five minutes at a time.
So, what did Cal gain by letting him come (even though he knew he might leave)?
Good will, as noted above.
Plus he got to innovate, which Cal loves. I suspect he saw that the top football teams have a similar arrangement with kids (especially QBs - the gridiron equivalent to a PG) where they enroll early and get a spring practice under their belt. This was what HD was getting.
So, get over it. UK lost zero, zip, nada by HD coming and practicing, even if he doesn't come back. And if he does return, Cal may have stumbled upon a way to make OADs more like Sophomores during that one season that they do play (remember, HD is different in that he can go pro as a freshman because of his situation - a kid graduating and enrolling early normally cannot. But maybe they can be like a football player who comes for spring practice - I don't know - but wouldn't that be nice?)