NM in Firehouse

I'm in the process of upgrading/moving the service at the fire house, as well as correcting dangerous stuff and bringing it up to code. I see a lot of Romex in there, does it all need to go, or is it grandfathered? It's a wood-framed building but is capable of more than 100 persons. I know MC cable is required today, but is the Romex grandfathered or does it all have to go? All work done after the mid-1990s is in MC cable or in conduit.