When one studies human phylogeny, we see that it is rare for just one species of the Homo Genus to exist, and oftentimes, a new, slightly better evolved one emerges from the ancestral stock. Applying the Darwinian concept of survival of the fittest, this new species successfully competes with the older one, and because of having adapted to the new external stimuli that may appear globally on the planet, and optimum utilisation of available resources, will drive the older species into extinction.
The new species is expected to be taller, bear less body hair than the average Homo sapien, smaller mandible and maxilla, and possibly, smaller arms.
2) The human demise theory is a possibility if current urbanisation trends continue. One might even apply the concept of insular evolution to humans. Insular evolution occurs on islands, and due to stagnation of the genetic pool, the species eventually goes extinct. If one considers the entire planet as one island, due to the accessibility of every stretch of land in existence, and due to progressive rises in interracial reproduction, the genetic pool of humans could also stagnate.
3) As for Creationism, whether by God, or extra terrestrials, I think the theory is pure bulldandruff. There is not a single nanoparticle of evidence that supports this theory, and all evidence available points to Evolutionism being correct.
So in conclusion, I believe that the Human race has two options- evolve, or die out.