By all accounts, if your kegerator's lines are clean and the kegerator is working properly, you can keep a keg of beer staying fresh for up to 6 months. 4 months is more likely. If you have to leave your home bar for a while, it is recommended to disconnect your beer and gas lines while you are gone. If the beer flowing from your kegerator is un-pasteurized, it may go bad sooner. Now, all of this assumes that you are powering your beer with CO2 or NO2. If your beer is powered by an air pump, you have about 8 hours to a couple of day if you are lucky.