Who could Riley find at this point in the year he could bring in as an OC that would do as good a job as Riley?? I think for 2017, Riley will have to suck it up and do double duty. He will prolly look to add an OC for 2018. I could be wrong though.
It wouldn't surprise me if he's always the play caller or co-play caller like Urban Meyer. He has to have an offensive coordinator though, so he can do head coaching duties. I bet they move people up/around for now, and the double-duties get shared like Bob has done in the past.
Remember, Cale Gundy is only coaching inside receivers while Dennis Simmons is doing outside receivers. Maybe Dennis takes over all receivers. Cale moves to either offensive coordinator for this year, or since he's currently Assistant Head Coach, he focuses on assisting Lincoln in head coaching duties so Lincoln can focus on offensive coordinator.
I agree that they don't make a rush position fill. There are enough coaches on staff to take care of all duties without Lincoln being the one that takes the brunt of the blow.