The league is an offensive league. Unless Vrabel decides to bring in a coordinator that can develop a QB and run a more modern offense not much is going to improve to there point we can compete at the highest levels. There will no longer be a running back that can carry the team. No experienced line to block for that non existent running back.
You could always hire and offensive minded coach with a track record of developing QB's. Let him hire a Defensive Coordinator to run his defense.
We could do worse for sure but if he leaves it isn't the end of the world. Could be a good thing.