I am pretty sure we would all be dead in about 8 minutes or so if the sun suddenly dissapeared. This planet would freeze pretty quickly. Also, Earth would be knocked off its axis and be sent who knows where as it is no longer affected by the gravity of the sun. Plants, animals, and humans would all die at pretty much the same time with only a few single cell organisms if that which would be left on the planet after such a cataclysmic event. 

You are correct in saying that our brain (reason) is our primary survival mechanism. We do not get "help" from animals though as it is only through our utilization of animals and plants (a process that involves transforming them into something usuable such as a good) that we can survive.

I'm an atheist so I don't regard humanity as special because of a divine mandate. Rather, the souce of my preference for humanity (and the source for most people I would imagine even if they don't explicity state it) is simple self-interest. I am more concerned with human life because I am a human. This is a rational stance as well since I rely on humans to survive/thrive just as all humans do with few exceptions. Once again, however, I must state I am confused with your attempt to juxtapose a hierachy on human, plant, and animal life. Humans have to exploit the Earth which includes animals and plants in order to survive. This is just a fact. You can attempt to reason which is most important, but the question is as I stated "most important to whom?" Humans need to display self-interest and a preference for their survival over the survival of plants and animals in order to survive. It doesn't matter if you like that or not it is the nature of reality.

If a human really became so warped in their thinking that they would be willing to destroy themselves because they falsely belive that humans are harming the planet then they have every right to take their own life. If they try to take the lives of others, however, based on their irrational belief then don't be surprised if people rightly try to defend themselves. I'll ask you and this person if they are stilling monitoring this thread, what makes plant and animal life so special to you that you would be willing to kill off a perfectly healthy species that is, itself, considered to be part of the animal kingdom at least in origin. It is not the stated goal of humanity to eradicate all plant and animal life so what is this supposed threat that you are fighting against?

One could ask where's the "fairness" in one species, humans,getting priority over thousands of others?

Of course we value our own kind over others, we're programmed to.

Honestly, things like humans repopulating species on other planets and such, that's all a bit far fetched and distant compared to the here-and-now reality of our destruction of thousands of species.