Prevent cursor from leaving screen when graphic tablet is turned off
Pressing the power button on a screen is really not how you should be "disconnecting" it. Your monitor and computer work together to communicate power states and connection states when you use them correctly.
Use WIN+P to control which screen(s) should be active in a given configuration. When a screen is disconnected, it will turn itself off given its power settings, and of course it will be darkened and windows or your mouse won't be routed to the disconnected display.