I don't think rock is completely dead, but where there are people, there are trends. Every trend has a peak and at some point, there is a revival. Think of classical music, it's very old and there are still concerts, even if the peak is obviously long gone.
People simply want to try and test new things. Combine old things in new ways, etc.
Rock is no longer a wild youth, but it's not dead yet either, it's grown older, more mature, it no longer has to play at every party.