Sooner or later, disasters such as an asteroid collision or nuclear war could wipe us all out. But once we spread out into space and establish independent colonies, our future should be safe.
However, we can still within the law, by using matter/antimatter annihilation, at least reach just below the speed of light.
With that, it would be possible to reach the next star in about six years, though it wouldn't seem so long for those on board.
Any one of my friends wants to chime in on that?