A person last seen at any site within the area proclaimed by the Governor on November 5, 1985, to be in a state of emergency as a result of the flooding in this state on or about November 4, 1985, whose body has not been found or identified within six months of the date last seen at such site, and who is unheard of by those who, had he been alive, would naturally have heard of him and whose disappearance can reasonably be believed to have been caused by such flooding shall in any case where his death shall come in question be presumed in law to be dead, in the absence of proof to the contrary or unless proof be made that he was alive within that time.