Absence of a proposed operative cause can establish absence of a ruling only when reliable evidence confines the ruling to that cause. If other independent causes exist, failure to find one does not negate the legal conclusion altogether.
Presumption of continuity (istishab) retains a previously established condition until an authoritative change is shown. It can protect an existing right from baseless removal, but it does not automatically establish every new right against another person.
In the case of a missing person, preserving existing legal consequences of presumed life and creating a new inheritance claim for someone else are different questions.
Mere failure to prove a claim is not itself affirmative proof of its opposite. Preserving a settled state, establishing a new entitlement and negating a ruling through exclusive causation require distinct arguments.