Only if there is not God and He does not love humanity would we have to attempt to look elsewhere to ensure the human race does not die out. But so many people who advance space travel for this very existential reason think that in doing so humanity can somehow escape the inherent failures of humanity.
If we could travel to other habitable planets, those new societies would soon be beset by the very problems humans have on this one.
Happily, there is a Creator God and He has a plan for humans to transcend their failures. However, the step that is in the immediate future is not so pleasant. It involves allowing humanity to fully experience the fruits of following the god of this world. See Revelation 12:12.
Genesis 1:28 - And God blessed them, and God said unto them, Be fruitful, and multiply, and replenish the earth, and subdue it: and have dominion over the fish of the sea, and over the fowl of the air, and over every living thing that moveth upon the earth.