I want my Mac to disconnect from my TV when I turn TV off

Hello. I have my Mac connected to my tv using a dvi to hdmi cable. I also use the Mac display it came with. The problem is that when I change my TV's input or turn my TV off, my Mac doesn't disconnect from the tv so I end up with half of my desktop missing. Is there a way to make the Mac disconnect when I change the tv input or turn it off so that all my open windows move to my Mac display ? It's 2012. Thanks

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