Yeah, if you're a fringe first-rounder with obvious and possible areas for moving up -- not "he's short" but "he needs to be more aggressive consistently" or "he needs to put on a few pounds and be more solid on D and get rebounds" -- it seems like a high reward/low risk move to come back. Especially if you can get your degree. You're giving up the chance that one of the last few teams will take you and risking that your stock will drop. But if you're really a fringe pick, there's not a great likelihood that you'll get picked, and DJ and Mo have the kind of skills/height that just don't go away. It's a bigger concern, in my view, if you're at 10-20 and trying to get up into the top 5 or ten than where they're at now. Maybe the biggest concern would be if they shoot poorly next year. I'd like to think that there's probably a better chance that they'll shoot similarly and fix some of their eminently fixable issues.
Also, I think this probably looks quite different if you came into the year thinking about the NBA vs you came into the year just trying to get minutes or stay on the court.
But we'll see. It would make sense for them to go to the combine, etc., if they get the chance. Even if it's just a practice run for next year.