Same scenario happened to me long time ago (I think 2006) in SFO. Lots of residual weather cancellations throughout the system due to a storm in DEN and my SFO to EUG flight was cancelled and UA offered a bus the next morning with hotel. That being a 8+ hour drive I pushed back hard and eventually got put on AS/Horizon via SEA the next morning still getting me back to EUG before the bus would have. Only myself and 2-3 other parties near the front of the line at the gate seemed to get this option though due to capacity on low AS, most got stuck with the bus.