I think it's "critical fail"

Kind of, but I think that's an altogether different question. The tree question is a philosophical one, basically asking whether sound is an objective element of reality or a subjective perception. The observer question is a scientific one, asking what conditions cause the interference pattern to collapse into two lines.

Yes, for example a photodiode can make an observation. Or a computer, or a photographic film.

The $800k house figure includes interest payments. So the value of the home will be much, much less than $800k.