What about a triple ADR failure?
Precisely what I also think, but apparently its unwise to think of such things!
First, total ADR failure is wildly improbable.
Second, even when it has happened it is still possible to fly the plane by turning the systems off.
Third, as such incidents have shown with ADR failure communications are important to get independent confirmation of airspeed.
Finally, I do not recall any ADR fault that has been found to be the primary cause of a hull loss.