> land itself is worth about 35-50 percent of the house depending on location

This is not always true. (Trivially: your land is declared a superfund site. Less trivially: fire sale.)

> there are never situations where the value of the house is worth zero

I guess a decade and a half is all it takes to forget.

It is entirely possible for land that house stand on being nearly valueless. Think of really rural or low demand area. And on other hand house it self being expensive to take down. Maybe containing mold or asbestos.

The cost of getting rid of the house - or other liabilities - is sometimes higher than the value of the land itself. There are situations of zero and even negative value.