Its possible. In the underwold yes! Depending if his widow's sister is also dead.

Why would a dead man want to get married unless his widows sister is also dead.

It's illegal and very scary.

The Marriage Act contains the following provision: 28 Any legal provision to the contrary notwithstanding it shall be lawful for — (ii any widower to marry the sister of his deceased wife or any female related to him through his deceased wife in any more remote degree of affinity than the sister of his deceased wife, other than an ancestor or descendant of such deceased wife; (ii any widow to marry the brother of her deceased husband or any male related to her through her deceased husband in any more remote degree of affinity than the brother of her deceased husband, other than an ancestor or descendant of such deceased husband; (ii any man to marry the sister of a person from whom he has been divorced or any female related to him through the said person in any more remote degree of affinity than the sister of such person, other than an ancestor or descendant of such person; and (ii any woman to marry the brother of a person from whom she has been divorced or any male related to her through the said person in any more remote degree of affinity than the brother of such person, other than an ancestor or descendant of such person.

Source: http://www.doj.gov.za/salrc/reports/r_prj109_marr_2001may.pdf

If he has a widow then he is dead and can't marry anyone, including his widows sister.