The defensive philosophy is derived from Huggins and Martin, right? Granted, I'm far from an expert in basketball, but makes sense the preferred defensive principles should not be overly difficult to teach (the question is do you have the right personnel to run)?
In terms of offense, so long as we have Underwood, I think we'd be ok. Sure, you want a good tactician on the sideline, but don't think Walker is a slouch there (just needs homework with Underwood system) ... and then you still have two spots to find your ace Chicago or national recruiter and another specialist or hybrid recruiter/tactician.
The world is not ending, folks.