Question for those who know better than me — AIUI if UA cancels your flight you can get a refund even on a nonrefundable ticket, so theoretically wouldn't it be possible to convert a nonrefundable credit into $$ by booking a flight for a day with weather that would almost certainly end up being cancelled (e.g. something like the last LGA-IAD of the day when there's thunderstorms on the northeast, or DEN-ASE the day of a snowstorm), and then getting the refund when the cancellation happens?