hello n welcome ....
first of all use of magnet is commonly done by physician and during PROGRAMMING of pacemaker defibrillator. usually use of magnet done by physician in many occasions therapeutically.
if it happens by mistake or unknowingly even then death is unlikely. becoz magnet usually fix that pacemaker defibrillator in a fixed rate or programme.
i think whatever they have done may be therapeutically needed in that particular case.
that is the reason its usually says that person with defibrillator/pacemaker should avoid MRI
/SCANNER in airport. that can cause malfunction but death is unlikely.
good luck ....