Ok, this info is proly so far out of date as to be a joke, but.....
It USED to be that if nothing was heard of a person again for 30 years the records were destroyed.. But that was in the good old bad old days before putors and was almost certainly because it was impoosible to store that much info !
Nowadays I would think it is almost certainly 100 years before automatic deletion would occur ( that is of course a wild guess but one based on certain info relating to work I was involved in about 10 years ago )