"I'd say nothing in this solar system is fit for colonization until we become far more advanced. Let's put the idea aside for another million years and hope we don't nuke ourselves into extinction."
There you have the future history of the human species. There are a few moons of the outer planets which have liquid water, due to heating factors such as friction, and so not relying heavily as we do on the Sun for warmth. On these moons it is possible that simple life may have developed - possibly microorganisms.
I personally believe that humans will not be around for billions of years but, just in case, we will have to allow for solar expansion. The Sun will expand almost far enough to engulf Earth, which will, however, have been long incinerated by then. Then, these moons will have been warming to greet us (sheer anthropocentric nonsense
) anyway, they will be at habitable temperatures. Unless water will have evaporated, we may find aquatic environments, with no land.
Before then, we should have taken action to avoid asteroid impacts. These may be "next week" in comparison, and a danger which we must take seriously. Our travels around the galaxy centre take us up and down through the galactic plane, and it may be that when crossing the galactic equator
we are in much greater of impacts. There is evidence for a cycle of 26-30 million years when danger may be greatest.