Well, they are difficult questions to answer in a short space.....
Given the current environment, I see no reason for apes to evolve. Humans supposedly evolved due to climate change and the loss of habitat. Monkeys on the savanna instead of in the jungle.
While I am as excited to be anally probed by aliens as the next guy, there is certainly theoretical basis to state that comet collision or extraterrestrial visit could have effected evolution, as either of those could change habitat or the like, or introduce new things a person needs to adapt to.
Creatures are changing over time, the changes are just so slow and small, they are nearly unobservable. Plus, with the enormous human population, human evolution should be at a near standstill. There is no survival of the fittest in human society really, and any genetic adaptations that any one person may form would be nearly impossible to spread amongst the entire population of humans. Plus with so many competing genetic differences, many of these types of traits are washed out. As I mentioned before however, look at native americans prior to the arrival of the europeans. They lacked resistance to the diseases of the white man. Now they have the same resistances, even if they have never interbred with other races. This is evolutionary adaptation. There are other examples. The average height of humans has increased over the years, and other minor differences.
As far as cockroaches go.... well, they are nearly perfect organisms like most insects. They have adapted incredibly well and can survive in nearly any environment. Their method of reproduction limits genetic variation and limits genetic competition.
Of course, any evolutionary theory is going to have SOME holes in it that are difficult to fill with anything more than theory, because it is a difficult science to test and find empirical evidence, but we can make sound theory by testing in similar areas and applying other known science. As I said, microbial research is a good field to apply to the study of genetics, because adaptation and evolution of germs and microbes happens VERY fast, as they are very simple organisms. We can apply many things we learn from that to complex organisms as long as we use fossil evidence and any other evidence surrounding us in the natural world.