Contingencies: Keeping Your Options Open
Certainly a nuclear war, a worldwide fatal contagion, or a global zombie apocalypse would all be difficult trials to endure. An ice age might push civilisation to the very brink. But Earth abides, and humans could too. In the near future, the only catastrophe that might require the complete abandonment of the planet, would be an extraterrestrial strike -- a comet, asteroid, or equivalent large scale impact.
Should such a planetary catastrophe occur, one would wish to have a convenient launch pad for an orbital craft capable of carrying one's self and significant others. One would also need a destination in orbit, where one could "freshen up" and restore one's natural vigour and vitality.
A missile silo home such as the one pictured at the top of this entry, provides both a rocket launching platform and a convenient aerocraft runway for quick access, if one is caught away from home base when news of the unthinkable arrives.
Fortunately, robotic habitat-building apparatuses are being developed which will allow you to construct your Lunar or Martian habitat over a 24 hour period, using a robotic contour crafting robot.
Parenthetically, the same robotic contour crafter could also be used to build an underground missile silo home & retreat, if none were available. International treaties are causing such valuable properties to become scarce.
Regardless, try to keep all of your options open. Most types of apocalypse will allow you to continue to reside on the most beautiful and life-loving planet in the solar system. But some types of doom will not permit that.
Hope for the best, prepare for the worst.