To explain that *sightly* better, there's no actual indication that a source has been lost. OBS simply keeps the last frame until the next update, and if it doesn't get updates anymore, it just keeps that frame forever. That's pretty much all you have to go on.
So if there's motion that suddenly stops, that could be useful. Or if the camera driver substitutes something that is clearly not a valid image, that can work too. But if it's something like a security cam staring at an empty alley, that simply keeps the last frame, good luck!
In the last case, maybe you can have a clock in the corner of the camera shot? (like, a physical clock in the camera's optical field of view, not an overlay in OBS) So when the clock stops moving/changing, you know it's dead?
