How to sanitize interior after long-term rodent intrusion?

What???
There had to be more to it than that. Maybe they ignored their symptoms, maybe they had some crazy religious "God will heal me" beliefs and never went to a doctor?

Not necessarily.
Hantavirus early symptoms can appear to be like influenza, and if not treated it causes severe respiratory problems and can lead to death.
Even though this is probably very rare, dealing with rodent urine and feces is nothing to take lightly.