Assuming everyone does stay an extra year, that may be a good problem to have. Though I'd bet at least a few guys either leave after their "senior year" to play at a pro-level (NBA or Euro), voluntarily transfer due to lack of minutes or transfer to play up a level.
I think at center it is more important to get a younger guy (assuming Lakhin is probably gone) then it is to maintain class balance. Koval is gone after the year no matter what, we don't want to have another guy also leave and need to add two centers again next year. Ideally, we add a JR (Collin Smith would be nice) and a developmental SO/FR at center.