You should assume that the tank let in co2 prior to running out. You can disconnect both the gas line and beer lines and assume that the beer will sit on gas until you refill. There are 2 ass u me pieces in there. I assume there are no leaks at your keg posts or lid .. yes? If it only carbed to half a volume prior to gas running out, it should sit at half a volume until you get more gas on it.