Kubiak did a good job today, but it would be a really bad idea to tell any head coach, including Rizzi or a new guy, that they have to keep Kubiak. You let your HC pick their staff anything else is a really bad idea. And frankly, I doubt any good HC candidate would take the job if you forced an OC on him.
As far as Kubiak, he did a good job today, but he's also done a lot of questionable things this year. I'm still not convinced that there aren't better OCs out there, but he has the rest of the season to prove that he is.