It is basically a scientific certainty that there are other habitable planets out there.
Which is damned-all use unless we have a credible technology for getting non-trivial numbers of people there. ("Non-trivial" being on the order of hundreds, though a lot of that necessary genetic diversity could be shipped as eggs and sperm.)
Currently, the only credible proposition (note : "credible" meaning "doesn't break any of the known laws of physics") is for "generation ships". And by the time we have that technology sufficiently proven for people to risk going out to [insert name of nearest star with potentially-habitable planets], then we'll also be able to scatter ourselves sufficiently around the solar system for instant species death to not be a consideration.
But we're a long way from that.