I wonder if there were time for the hypothetical travel to go to the airport earlier in the day, could they try going to the ticket counter, explaining their situation, and seeing if they can get a free same day change to a later flight. I know the A list standby benefit only applies to earlier flights, but WN staff also seem to have a lot of leeway to make 1-time exceptions for other circumstances, I don’t know if that applies here. (Plus even though it’s a standby benefit, in my experience, as long as the earlier flight has space, it works out as a same day confirmed change. I don’t know if we’ve had any reports though of people trying to use the A list standby benefit for a later flight).
Though if trying this out, this hypothetical person perhaps might want to purchase a refundable ticket on another airline in case the answer is no.