I have wondered, what'll happen when we destroy our planet or it becomes uninhabitable for human life? Is there another option than the complete extinction of the human race? Can anyone give me a logical response?
what'll happen when we destroy our planet or it becomes none-habitual for human life?
Very pessimistic idea.
We lack the technology to tell if a planet orbiting another star could be lived on by humans. We barely have the technology to detect some planets orbiting a small number of other stars (compared to the number of stars in the galaxy).
The term for these planets is exoplanet and Wikipedia says we have detected about 3750 to date orbiting about 2800 stars. As there are somewhere between 100 and 400 billion stars in the galaxy, we only know a tiny fraction of what's out there.
We have a very limited basis for listing some planets as possible candidates for supporting some form of life, but, with all respect to the serious scientists doing this work, this is nowhere near knowing if they really can support life at all, let alone humans.
So your question's answer is : we don't know.
We cannot travel fast or far enough at present to reach another star in a reasonable time frame and we also could not do it with enough people. We do not currently have any reasonable expectation that we will be able to do that in the future.
So even if we knew of a suitable planet, it would be unlikely we could ever travel there to e.g. colonize it.
So we're stuck here so keep recycling. :-)
Is there another habitable planet in our galaxy?
What constitutes habitable? Oceans, lakes and rivers, soil to grow plants, oxygen to breath, a magnetic field to help maintain the atmosphere, plate tectonics, an ozone layer to block UV rays, not too much or too little gravity, or too much or too little air pressure. No poison in abundance Oxygenated, not Anoxic bodies of water or too many hydrogen sulfide producing bacteria, and lets add, just for fun, no 350 kph winds or 10 inch hale stones on a daily basis or dust storms that could choke a bantha.
On, and one more thing, if a planet meets all those criteria, especially the breathable oxygen atmosphere, there's probably life there already, and so there's the "They were here first" problem and life isn't always friendly, we might be toxic to them or they might be toxic or hostile towards us. That's a problem with potentially habitable planets with Oxygen atmospheres. If there's Oxygen, there's probably life and if there's life, that raises questions, not just moral ones, but safety questions as well.
That's a bit of a catch 22 in the habitable world question. If there's oxygen there's probably life and if there's life, we need to be very careful before we set foot there. The odds of finding a water/oxygen atmosphere world with no life is pretty remote.
But to answer your question - habitable planets? Nobody knows. There's no way of answering this question with what we know today.
Is there a potentially habitable planet in our galaxy?
This one, almost certainly yes, though we don't have good enough telescopes to say yes for certain but there's enough planets out there that a few of them are expected to be "Earth-like".
Earth-like, meaning, A rocky planet with plate tectonics, an atmosphere we could work with, oceans, continents and a magnetic field. Such a planet could in theory, be terraformed and become Earth like.
While terraforming is theoretical and there are significant unknowns and it would take some time, there's probably no shortage of Earth-like planets with roughly the right range of solar energy, gravity, atmosphere and liquid water.
With technology we could live in lots of places.
Mars, Titan, the Moon, Mercury, Venus (in acid-resistant dirigibles), Ceres, Icy bodies like Pluto or other Kuiperbelt Objects. Those are all livable, with proper technology. Colonies would likely be small at first, and it's perhaps not what I'd consider a fun place to live, but drilling a hole into the ice inside Pluto, for example, with an energy source, perhaps fusion, or if closer to the sun, solar power. Settlements would be possible and not even that far beyond our technology today. It'd be expensive to get all the necessary equipment out to the whichever location you choose (Lots of people have their eyes on Mars - but other locations would work too). But such settlements aren't too far out of our current ability and we'll likely begin to see them perhaps in the next 50 years or so.
Traveling 20 or 30 light-years is hard.
If you want another planet, not just a small colony living on Mars or Ceres or Titan or Pluto (Ceres would be fun, you could probably jump like 100 feet in the air, or lack of air I should say) . . .but I digress.
But if you want a real planet, that is another Earth, the hard part isn't finding one, the hard part is getting there. I'm not going to say anything more about that other than inter-stellar space travel is really really really hard. Gonzo, crazy difficult.
Outside of tiny settlements, Earth is it, for the foreseeable future. We may be able to identify other planets in the not too distant future, but getting there is an entirely different ballgame.
What'll happen when we destroy our planet or it becomes none-habitual for human life? Is there another option then the complete wipe out of the Human race? Can anyone give me a logical response
Other scientists have pointed this out as a reason why funding for astronomy because, in time, it could play a role in saving our species. Stephen Hawking, for example. So you're not the first to think about this.
"I believe that the long term future of the human race must be space and that it represents an important life insurance for our future survival, as it could prevent the disappearance of humanity by colonising other planets."
The good news is, actually wiping out our species is hard. A large meteor impact like the one that killed the dinosaurs is a rare event - once every 100 million years or so for one that big and now there's a good chance we'd see it coming. Mankind killing events are statistically rare.
The bad news - finding a 2nd Earth like planet and getting there is very hard.
I'd advise not worrying cause worrying about the destruction of mankind strikes me as unproductive, but you can petition for more money to NASA or Space-X or other space exploration organization of your choosing.
I would like to add some points to StephanG's answer.
If you are just considering another habitable planet in our galaxy why look anywhere else other than in our own Solar System?
Mars is half the size of Earth and also there are many proofs saying that there was flowing water on Mars with which we can say that terraforming Mars is quite possible. There is even this Wikipedia article on this.
Then there is Titan which is Saturn's moon. When the Sun is nearing it's ending and becomes bigger and turns into s Supergiant, there is a possibility that we could colonize Titan. Here is a Wikipedia article on this.