United delayed boarding on flight from EWR to JNB due to "waiting for the crew", and then a further delay on the tarmac for unspecified reasons resulted in the crew timing out and the flight being canceled. Passengers were rebooked on the next flight, which is a full 24 hours later. As of now, they lost paid-for seat assignments, which they've been told will be refunded - but they don't want the refund, they need the better seat!
1) Is there anything to do to get priority on getting that requested seat? (No status, but passenger requires wheelchair assistance)
2) What kind of compensation should the passenger expect for the cancelation?