I'll attempt to answer what I'm sure you intended as a rhetorical question. I will also do one better an answer with no statistical evidence but rather mere anecdotal evidence, which is always strong.
But, anyway, from my point of view I'm not sure it's worth testing the waters b/c I'm not sure there'd be any logical reason to leave. If you were a potential lottery pick, for the most part, we'd be hearing those whispers already. If you're not that high but are still likely to get drafted it likely means an NBA team either believes you fill a specific role -- in which case you're still going to be a player who can fill that role a year later -- or that you have the potential to still improve significantly.
So, where it makes sense to me to consider leaving is when one or more of the following things is true:
- You want $$, don't want to waste time in college and are fine if the NBA doesn't work out and you end up in Europe, etc.
- You are a lottery pick and the guaranteed money is tough to pass up.
- You had a big year and based on certain factors your stock is unlikely to rise further (see Ennis, Tyler).
- You're a long, athletic wing-type or maybe an athletic big that can carve out a 10-year career based on a few key skills/physical attributes and potentially can garner enough minutes to see your offense evolve over time.
So if those things are true, give it a shot. I'm cool with it. What i don't really understand is how either of the following types leave:
- You have a world of athleticism but major holes in your game that keep you out of the lottery and potentially out of the first round. The NBA doesn't have much patience, IMO, and if you have serious upside offensively but have yet to realize it, my opinion based on exclusively anecdotal evidence is that you're better off trying to use a ton of minutes and touches in college to improve your stock and, more importantly, your game.
- When you haven't stood out on a team that is OK but not great. If you're on a Kentucky team that goes 8 deep with first-rounders, fine. But on this Cuse team, if you're shooting 37% and playing well but not necessarily standing out, then it would seem to me you have work to do.
So, for me, if you're in the shoes of either Lydon or Richardson, it would make the most sense to me to block out all the NBA junk and come back as better players on a better team and go from there. I just feel like the question is not as much about when and where you get drafted as it is about how good are you when you get there. Just my opinion.