As we know, we need to read the temperature when we try to cotrol the TEC and fan. So if you disconnected the camera, we can not get the temperature. In this case, there are many other problems with arbitrarily controlling the TEC.
According to our experience, Just stop the cooling and let him warm up naturally. It will be fine.
I´m not sure I can follow your argumentation. Keeping the fan running could be entirely decoupled from the camera being connected to software or not. As soon as I plug in the 12V supply, the fan starts running. So this obviously does not depend on the camera being connected to software. The camera should "simply not care if it is connected or not" and keep the fan running as long as 12V are provided. Regarding the TEC, I would think that the control can (is it not?) be done from within the camera, avoiding unintended changes of the cooler status, when not explicitly initiated by the user. The camera temperature is provided by the camera, not by the software. So I do not understand, why one needs to have the camera connected to keep a set temperature controlled. As an example, there are focusers which display the temperature on the device upon connection to power. No need to connect with software (which might use the same temperature for compensation, etc.). The current temperature setting as well as the current cooler status can be managed by the processor in the camera. There even might be smart technical solutions (maybe simply a capacitor of sufficient size to delay the power off on the controller) to run a tiny shut-down script when the camera is physically disconnected from 12V and USB, resetting the cooler status to off, so that it needs to be activated again upon re-connection of power.
Just some thoughts/suggestions...