Liability and/or negligence must be proven. For example, if I slid on ice on a property and injured myself I must prove negligence. If I slid on an ice pool from a leaking gutter the homeowner had not fixed, they would be negligent. So will the staircase be considered Jonah's negligence?
Since Jonah is a wealthy man, I tend to believe Jonah is covered by a large umbrella policy. Whatever the homeowners policy falls short of covering monetarily, the umbrella policy could kick in. Two policies instead of one.
Liability doesn't have to be proven. There is no dispute it happened in the house and involved a fall.
The homeowner has liability. If your dog bites a passerby, you are liable. If someone slips on ice, you are liable. If someone falls over a balcony banister, you are liable. If someone falls down stairs, you are liable.
JMO