I think with all the work you have put into this world and these sims it would be a shame to let a burning rock from space ruin it all for you. Personally I think there are enough catastrophes in RL, both man made and natural without having to worry over such things in game. Perhaps it wasn't the original intention for the game but a lot of people use TS3 as a means of relaxation and I can't think of anything more stressful than watching such a scenario unfold. As you say some things are more important than money and I think saving the lives of those two sims, especially ones you have put so much time and effort into creating, might count as one of them :)