As long as the leisure yields hold out, LAS is still on the screen. There is non-stop demand from nearly every good size city in the USA for a non-stop flight to Las Vegas. With that said, because of the demand and the non-stop flights to everywhere, you will still see it as a connection point.
PHX is not going anywhere, it is the key to America West's west coast service. PHL is the biggest metro area of all the hubs, and the key international gateway in the east. It isn't going anywhere. Don't forget DCA, where now America West is a dominant player. In addition to the west coast flights, its got a lot of slots on east coast flights. This city generally commands higher than average fares, so its a keeper, maybe not a hub, per se, but a big destination.
PIT is done in the long term. CLT is on the bubble. Its close proximity to PHL hurts it. There isn't as much local traffic in CLT as in the other hubs. For now it is a keeper, but for now it is a keeper.....as long as the yields stay high, service will stay....but in the long term?! Who knows.