Have you started music playback and turned off the TV before, and if so, has it worked? For the same length of time?
That sounds like your PC lost its HDMI connection and hence decided it couldn't play audio anymore. While MC shouldn't crash, basically the rug has been pulled out from under MC. It effectively lost the driver that enabled playback. There have been discussions about this stuff before. I think the only way to fix the issue if you really want to turn off the TV was to use one of the HDMI curing devices. Doctor HDMI or something? Those devices maintain an HDMI connection to the PC with the correct parameters and hence audio playback continues.
If your AVR acted as an HDMI endpoint, rather than working as a Passthrough, then the PC may continue to work. But then you may have video issues, depending on the AVR capabilities, whether it wants to alter the video signal when not in Passthrough mode, and so on.