Subbing out aircraft is being cut down some, but it'll still happen. Typically if you see your portion of the trip marked as ontime but the originator is running 2 hours behind - they are going to sub it. They'll also overfly cities if weather is too bad or stub flights and just get rid of specific segments of it. I've seen them take a flight that would be operating say LAX-PHX-ABQ-MDW and PHX would be messed up, they'll cut out PHX and just go LAX-ABQ-MDW.