i think they'll still be around for 2-3 years at least (if not longer) as they phrase it out slowly. from how pc are going, it seems that they want to move from pci to pci-express but the problem being that i dont think manufacturer's care to invest money to make a PCI-Express card/motherboards that doesnt offer any difference then the pci version (how many PCI-Express sound cards do you see?). maybe if there are more peripherals besides graphics card that can take advantage of the bandwidth then maybe we'll see a move to pci-express.
if you look at your pc now, what PCI card are you using?
before, we had the sound card, the network card maybe a usb card, but now that has all been integrated into the motherboard. if you need a sound card, you can get a PCI one and the PCI slot will be more then enough for it.