...the best insurance is to propel civilisation off-world and spread human & terran life across a multitude of worlds.

By itself a single 'cosmic liferaft' won't make it. Too many hazards. What's needed is firstly a true von Neumann machine that can replicate itself and any useful piece of machinery. A closed-loop rapid prototyping machine is being developed right now, so vNM isn't much further away once the support robotics is developed. Then we need a way of storing organisms in a medium hardier than DNA - too much damage from cosmic rays otherwise. Those organisms also need some sort of ectogenetic artificial wombs, logically. Then we need a system that can make cells from raw materials directly. As viruses can be made using a protein-sequencing machine this shouldn't be impossible.

Once we do that the final step is pretty straightforward - all terran lifeforms can now be replicated from raw materials, plus the humans have a machine that can make the tools of civilisation itself. These "Noah's Arks in Micro" can then be launched via laser micro-sail boosters to interstellar speeds and sent out to every star system with any kind of free mass in orbit to build inspace habitats if necessary or start colonies on terraformable/habitable planets. Once spread across a few thousand light years terran life is pretty much guaranteed continuity. If life can be wiped out on a galactic scale would would have seen galaxies exploding before now.

Adam