(a) If an appellant dies or is otherwise unable to pursue the appeal, the processing of the appeal will only be completed upon substitution of a proper party. Substitution will not be permitted where the interests of the appellant have terminated because of the appellant's death or other disability.

(b) The representative or proper party must file a motion for substitution within 90 days after the death or other disabling event, except for good cause shown.

(c) In the absence of a timely substitution of a party, the processing of the appeal may continue if the interests of the proper party will not be prejudiced.