In my experience, the tower is typically bapassed in the heating season. The tower rejects heat in the cooling season. In the heating season, we add heat to the loop via a boiler. Running the tower during the heating season would reject the heat that we just put into the system, and throw away money.
i service several systems like you described along the southern shore of lake Erie. They use Climatmaster water source heat pumps, small boilers, and cooling towers to keep the loop between 75df and 95df. Never drained the towers unless there was a problem. Using a Novar system to keep the loop active and alarm for high or low temp. Most of the air handlers are a pain to work on, usually in the ceiling of an office with white carpet and a glass top desk. Preety reliable system, as long as they don't overload the capacity of the loop.
Agreed, I have a system like this. We will drain the basins because they are not that big and can be filled quickly. But i make sure the louvers on top are closed and i make sure the spray pumps are drained. Keeping water running through the bundle will also keep chemicals in them. Also, you never know when you need to run the fans, even with out water spraying, the cold air will help cool the loop if you need them.. I have seen where some have drained the coils and did not do this properly or valves leaked...and they found broken tubes when they started up in the cooling season.