I imagine if someone comes up with a better page ranking algorithm they definitely have a shot at beating google.
Not a chance... about the same as Linux has at beating Windows on the desktop, in my opinion. It's too entrenched, too far ahead, barrier to entry to even get to a level playing field is too high...
I'd love to see it, to be honest. I hope beyond hope it will happen. But I think it's more likely to see something remove the need to search entirely than have a new search engine take out Google's dominance.