In the case of a catastrophic (and extremely sad) plan incident, there has to be some way to locate a black box in an unrecoverable situation, yes? A signal? Or blip? Or radar mode? Or is this something that movies and video games have made me think is possible.

Does anyone KNOW with 100% certainty?

If the indestructible black box is designed to be found – at all costs- and if there is nothing, it could be a point toward MH370 being blipped out of existence.