Nope. Mankind will peak at around 10 billion people, maybe more depending on how miserable people are willing to be before the proverbial feces start hitting the proverbial fan. Around this time we're not interested in space, because we're too busy killing everyone on the planet. When that's all done, it seems like we have enough space on earth again, so we invest in earth again rather than space adventures and the population will slowly grow until we reach 10 billion again. Murder all around the globe, once again. Rinse and repeat. Until at some point in the future the solar system itself is going to hell and by then we're too late anyway.

Now, this is all true UNLESS we can find a way to get Bruce Willis to go into hybernation for millions of years so that he can save us in the future. I think we oughta get a kickstarter going to freeze Bruce Willis otherwise he'd be too old for that shit.

Do I think mankind will ever inhabit another planet in out solar system?

Yes, the Chinese are already planning a moonbase, and they have the resources to achieve their goal. But the most exciting project is the 100,000 colonist city that Elon Musk and SpaceX plan to build on Mars.

They "can" consider that option...

But

If people think more about "sustainability and sustainable development", we can live on our own earth without any problem. :)

Just yesterday NASA announced the confirmed discovery of methane vents on Mars that are probably a geological feature, but given the associated discovery of water ice on Mars it has some at NASA speculating they could be caused by bacteria-like microbes. 

In addition, Saturn's moon Titan has liquid oceans of ethane and methane, and could be home to all sorts of interesting microbes or multicellular life. The Huygens probe confirmed this, but now we need to go back and have another look. 

Aegis, I like your thoughts. Especially on genetic engineering and on the threat from asteroids, which is not at all laughable.

But I have a different opinion on one point. I do not think that humans will have to stay alive in space for years. I think the ship will be unmanned during the voyage, which may take some centuries (but who cares). The settlers will only be born when it's there (and after the necessary terraforming measures). They will be bred in an apparatus that emulates the functions of a uterus. That first generation will have to be raised by robots. An odd childhood, but better than spending one's whole life in a can (like on a generation spaceship)...