It really is a freaking crime that we’re down to two species of Proboscidians, and both species are in big trouble. 70,000 years ago there were elephants all over the world. If you asked visiting aliens whether the monkeys with the broken rocks or mammoths ruled the Earth, they’d have answered mammoths with no hesitation.
That said, I agree completely with Blake. With no hominids, there’s no reason any other species would become a tool user. It’s not like it could never happen, but there weren’t any large brained tool users for the first 649 million years of multicellular life on Earth, so if hominids had went extinct it’s not like any other species would have “taken our place”. Our place is “large generalist omnivore”, not “large-brained tool user”. And there are dozens of species that fill that niche already–bears, pigs, racoons, other primates, foxes, dozens of other medium sized Carnivora alone, large rodents, and on and on.
There is something to the idea of a “niche”, and it certainly is true that animals that fill the same niche often tend to superficially resemble each other. But when you look at anteaters, pangolins, armadillos, aardvarks, and echidnas you can see the convergence–long snout, reduced teeth, long tongue, claws. But if pangolins went extinct you wouldn’t see aardvarks evolving scales to take their place.
To take another example, there used to exist large clawed herbivores–chalicotheres. There are all kinds of theories about their diet and habits. But nobody knows for sure, because they are now all extinct. And it turns out, in South America there was a creature that was completely unrelated to these clawed ungulates, but evolved a similar appearance and lifestyle: http://en.wikipedia.org/wiki/File:South_American_Homalodotherium.jpg. So, whoah, two unrelated creatures that evolved to fill the same niche. Except, both are extinct now. So there is definately a niche for a large clawed ungulate out there. Except, what creature will evolve to fill that niche? It’s very likely that the world will never see another large clawed ungulate, that no such creature will ever evolve again, despite the fact that it already happened twice.
So there’s no reason to suppose that another creature would evolve to become social tool users if humans never evolved, or become extinct. Yes, it could happen, but there’s no reason to think it would.