"Coach/Mr. Captain, if you decline the face mask penalty, the game is over. You're going to want to accept their penalty, and they'll accept the holding penalty, so we'll replay 4th down."
Don't give them a chance to screw it up.
Excellent, VALC, in this critical situation we may want to also involve K's coach and captain so everyone understands what did and will occur.
Possible procedure :
(1) Ask wing officials to bring both coaches out to be with their captains;
(2) WH sez' to the gathered group : "Guys, BY RULE, with both teams fouling as time ran out we can have an untimed down. IF the receivers take the facemask penalty it becomes a double foul and we replay the down, otherwise the game will end. Can I assume (looking at R's captain and coach) you will want to replay the down ?"
(3) Coach or captain's response :
"Ayuh, 'spect so"
or,
"Can't we just decline their penalty and keep the ball ?"
WH : "You could, but the kickers could then decline your penalty and BY RULE the game would be over."
Coach : "Ayuh, you're probably even smarter than our governor."
The ending of this game may be debated long and loud if both coaches don't understand what is about to happen.