I'm not sure I totally understand this line of thinking -- feels like a slight overreaction to the rash of players we've had going early somewhat unexpectedly (McCullough post-injury, Ennis at the right time but just not what we were expecting, Lydon after a so-so sophomore year, Mali seemingly out of nowhere, Grant when he couldn't make a 15-foot jumper, Bazely deciding to take his talents to the G League ...). But the thing all those guys had in common is that they were in pretty good shape to find a landing spot in the draft. All were first-rounders outside of Grant but it feels like he had strong intel that he would get guaranteed money as a 2nd rounder if he didn't go in the first.
What makes your scenario a little strange, IMO, is that Carey would have to explode onto the scene as would Hughes and then Marek, it feels to me anyway, would have to really just want to get closer to home. All three feel like possibilities -- and if Hughes and Carey explode this team would be unreal and likely a title contender. So, to that end, I won't complain if it happens.
But, Carey is only a fringe top 50 recruit -- not a bad thing and still a really solid get but not a top-10 guy. Plus, he's a 6-3 guard, which is a tougher pool of talent than if you're walking onto campus as a super skilled big like a Bazely. Hughes is a 6-5 small forward so he really falls into the same category in the sense that he's pretty small to be a 3 at the next level. And Marek could be close to a degree after his third year (were he to stay) and still is just scratching the surface as a player even though I know he's a little older than most sophs.
I don't know -- could happen, but those guys don't fit the same profile as the others that left early. Not saying you're wrong but I'd argue -- even though it's bucking the trend -- that we'd be more likely to have all three back than to see all three leave. Just my opinion, obvioulsy.