Originally Posted by
jkatzen
I'm sure Mr. Tickets' answer is the "right" one.
That being said, given that it's a medical issue and you're a platinum member, you might (possibly) have some luck convincing an agent or supervisor to allow your change after you're already in Minnesota.
+1
The other option if you need to make sure your friend gets home is to just no show for your return flight. He can check in on his own, board, and take the flight, and then afterward you can call DL to attempt to rebook it purchase a new ticket.
Of course, this method could be quite an expensive one.