Subarus usually just lose the horn. Presumably if airbag was inop you'd get an airbag light.
However, yeah, Subaru was forced to essentially give a lifetime warranty on seat belts after they failed to retract and the belts tended to fray. Those models are now so old most dealers don't know about it, so you have to stand your ground on that one.
I suppose if it applies to seat belts in Subarus and consider all the Takata airbag recalls in other makes -- I guess a clock spring could be similar IF it's actually triggering an airbag light.
OTOH in both the case of the '11 Outback and the '13 Highlander the owners wanted it fixed because they tried to honk at someone who was merging into them and discovered their horns did not work. They then felt unsafe not having that ability to potentially communicate with other drivers. So there's a solid argument to be made that a functioning horn is a safety item.
According to Google:
"Every state with an active vehicle safety inspection program checks for a working horn. If your state requires a periodic safety inspection, your horn must be operational to pass.States with safety inspections verify the following:Audibility: The horn must be clearly heard from a set distance, usually 200 feet.Accessibility: The horn button must be within easy reach of the driver.Prohibited Devices: You will fail the inspection if you use a siren, bell, or unreasonably loud warning device reserved for emergency vehicles.States with periodic safety inspections include:
Delaware
Hawaii
Louisiana
Maine
Massachusetts
Missouri
New Hampshire
New Jersey
New York
North Carolina
Pennsylvania
Rhode Island
Texas (safety requirements still apply in many metropolitan areas)
Vermont
West Virginia"