I think the fact that the Reddit management got to witness the rapid death of Digg and rapid influx of users resulting from it let them learn a valuable lesson at Diggs expense (at just how fast your users can destory you if you piss them off).

One thing I wonder though is where Reddit users would go in the event of such a collapse. I'm not aware of an established site in this format that's available like Reddit was available when the Digg collapse happened.