If the question is limited to the "next hundred years" only, the probabilty that humans still dominates the earth by that time is very high.. I dont think humans would be considered "endangered" within that span of time.. Right now actions to prevent global warming are already taking place and I belive that we will have the technology to stop global warming within a few decades.. About the issue of poplulation explotion, I think thats more of a problem of poor countries.. Poverty is the actual problem, not the world population.. If the population of a country continues to grow while its economy is in a near standstill or falling, the poorer its people will be... In fact if you look at almost all the rich countries you'll see that they dont have a problem with over population.. the US for example only have around 300M if im not mistaken... So yes humans would survive the next hundred years unless a giant asteroid hits the earth and blow evrything to pieces..
Oh and yeah, the idea of moving to another planet.. I dont think thats possible within the next hundred years.. Also, Neptune and Uranus are not a place that can support life the way we know it... And even if Mars can be our next destination, its hell of alot easier said than done.. think about it.. you cant just send a group of men and build a city on mars right? The thing is why move to another planet when we can save our own.. I think its the easier, cheaper and more rational thing to do..