Richard,
Assuming that your hot water dispenser is mounted in the same manner that mine is, there is no way to drain the 1/2 gallon tank without removing the unit. The problem with leaving water the unit is that it can freeze and break if the coach is stored in very cold temperatures. Otherwise there is no problem in just leaving it alone. If you never plan on using the unit, it only takes 10 minutes to remove it and get more storage space under the sink.
If my hot water dispenser failed, I would have to replace it or get a divorce, because my wife loves it. We use it for coffee in the French press in the morning, instant coffee, hot tea, or anytime we need hot water for cooking.
Gerald