I personally think that taking a chance on Riley is worth it.
I don't think they really had any other choice given the timing, and thus I believe it was planned all along, and was done this way so as to alleviate an even bigger meltdown by OU fans.
I believe OU is hoping that this means they'll have a HC for decades. It's a gamble for sure.
I tend to agree with this, the timing sucks for them, but it's clear they had a plan leading to this. He (Lincoln) has high risk (but manageable), but also high reward. If he works out, they'll have a young guy that can keep them there for a long time, if he doesn't, OU will be able to get about anyone they want. OU is a destination job and easily a top 10/15 job in college football. Also, at least for Lincoln's sake, he gets to inherit a team that is full of good/great players, the chance for him to have success year 1 is very good.
Any coach that has success at OU will be there for a long time. Nobody is using OU as a stepping stone (outside of weird Urban/Florida, or Saban/LSU examples, but even then, those guys won national championships before moving).
The Michigans and Ohio States and Alabamas and LSUs and Texases (Texasi?) and OUs of the world don't have to make the coaching decision out of weird loyalty paranoia. Leave that crap to the Techs and KUs of the world. By contrast, programs like OU are destinations. They go out and let other people figure out whether this guy can coach, and then they use their status and cash to turn Les Miles from a Poke to a Tiger, to turn Urb from a Ute to a Gator, etc. etc. This is just a flat out unnecessary risk for OU.
The only explanation here outside of just bullshit laziness on Castiglione's part is if Stoops' decision was unexpected. In which case, yeah, It's june. Keep the continuity for 2017 and then go have a bonafide search and hire a bonafide coach. But this whole thing just looks so crackerjack for a program like OU.