I could have been really annoyed by a similar situation had I not visited the Admirals Club a couple weeks ago.

I was flying SFO-JFK then LGA-PVD. I know i never should have accepted that routing. Upon arriving in JFK, I went to the Admiral's club to try to get a standby seat on a JFK-PVD. After finding out nothing was available, they noticed the LGA-PVD was cancelled anyway, so I would have to leave from JFK.

I would have been REALLY annoyed if I trekked across Queens to La Guardia only to be told to go back to JFK.

Other than the Admiral's club, I was never notified.