The point about accounting for uncertainty is very well taken. I had not considered possible asymmetries in the effects of uncertainty when writing this.

On longtermism generally, I think my language in the post was probably less favorable to longtermism than I would ultimately endorse. As you say, the value of the future remains exceptionally large even after reduction by a few orders of magnitude, a fact that should hopefully be clear from the units (trillions of life-years) used in the graphs above.

If I have time in future, I may try to create new graphs for sensitivity and value that take into account uncertainty.

That's an interesting point. I'm a bit skeptical of modeling risk as constant per unit volume since almost all of the volume bordered by civilizations will be empty and not contributing to survival. I think a better model would just use the number of independent/disconnected planets colonized. I also expect colonies on other planets to be more precarious than civilization on Earth since the basic condition of most planets is that they are uninhabitable. That said, I do take the point that an interstellar civilization should be more resilient than a non-interstellar one (all else equal).