Yeah, unfortunately it's kind of a no-win (or at least few-win) situation here. You don't want to root for Castle to come back, and there are a lot of ways where he underperforms but leaves anyway.
If Castle's stock drops enough that he would consider coming back, that reflects horribly on the program and we're going to have a hard time attracting any more of that legitimate top-10, one-and-done level of talent, on top of the fact that it would likely mean that his/our season went badly. Maybe we get NBA-level Castle as a sophomore, but that would be merely a hope and damage would already be done.
He may even be merely "OK" and leave anyway with his stock having dropped, which means a mediocre season this year and no benefit from him next year (think 2012 Drummond).
The only really great scenario is he suddenly finds it, is amazing the rest of the way, propels us to a deep run, and gets drafted high while demonstrating to future recruits that we are a destination for top 10 talent. But with each game that seems more and more remote.