I did notice that LibreELEC will go to sleep or kind of turn off if the TV is turned off. But it doesn't wake up correctly. I'm sure there's a setting to prevent it from turning off that I haven't found yet. I'm hoping that the waking up will be fixed eventually.
This happens because TV notifies board when it's turned off over HDMI CEC. There is a setting what to do in such case somewhere in System / Input (I don't have any board here ATM). You can of course disable powering down the board there.
Proper sleeping/waking is tricky, so it won't be implemented soon.