I think the big issue for us is that whomever we play at CB we will probably be fielding a CM (Hendo or Fab) at CB. Whilst Fab and Hendo have filled in admirably, particularly Fab, I think they both do much better with a proper CB beside them. In contrast, with Rhys or Nat beside them, I think they'll look even worse because they are probably taking some cues from who they are playing with and if it is an inexperienced CB then the coordination of our line, offside trap, positioning and marking and general awareness is probably going to be a bit average.
No offence to Rhys or Nat but they aren't at the level needed to just come into the team straight away and fill in when we're chasing top 4 and hopefully a title tilt in such a competitive league. Not saying that Rhys or Nat will never be good enough, but it's a bit too soon. They needed a more gradual introduction rather than just thrown in at the deep end.
I think we probably have to reevaluate our position on not brigingin in a CB. Are we really confident that we can't get in someone better than both Nat and Rhys? We don't have a lot of time either, so I imagine they'll be desperately trying to come up with a solution.