That's weird. Don't we get enough stories about Rust Belt economic hardship and Detroit real estate horror stories to know that property values don't always go up? Have we already forgotten 2008?
But it don't have to take a depression to create sinking house prices. In Sweden we had shrinking house prices between 1931 to 1981, with only three years (right after the war) when prices increased. The same period is the most economically successful period we ever had.
Why? Because politicians built a shitton of houses (and tore down a lot of crappy housing too). Nowadays people here too think prices always go up, not realizing it is a political choice. It may very well be the right choice, but so many doesn't even understand it is a choice in the first place.