It doesn't need to be completely burned to be gone:
"No redemption will be made when (...) Fragments and remnants presented which represent 50% or less of a note are identifiable as United States currency but the method of destruction and supporting evidence do not satisfy the Treasury that the missing portion has been totally destroyed"
"No redemption will be made when (...) Fragments and remnants presented which represent 50% or less of a note are identifiable as United States currency but the method of destruction and supporting evidence do not satisfy the Treasury that the missing portion has been totally destroyed"
Not that unlikely, in my opinion.