The general wisdom pretty much everywhere Ive worked is keep someone in the building 24 hours a day. I work in a 3 station cluster, and one station is live 24/7. The other two are another story. And these havent all been major markets. I think thats why so many CBS stations in Boston have overnight guys, and in other (even larger) markets thats not the case. Overnight guys at CBS in the rest of the country seem to be a thing of the past.
Where I work now we use maestro. Its incredibly unreliable, and it does something rediculous and goes off the air on a regular basis. Where i worked last used nexgen, and even that used to crash on me from time to time. And nexgen crashes are bad because they involve multiple computers. 4 run the air studio computer. (air studio terminal, the actual computer that plays the music, the stream computer, and the studio router)
But you only need one person to respond to these kind of problems. For weather there is someone on call, so a first responder to hold down the fort until he gets there, power failures, etc. A friend of mine who was doing overnights in NH actually saved her transmitter building from burning down (and kept her station on the air the entire time).
So anyway, think one person per building, and every boston cluster I can think of does this, except maybe medford and WFNX.