a superintelligence killing us all is a superintelligent, very large X-risk.
the superintelligence will tile its values in all directions; not just through space at the speed of light or faster, but also, if it can, by hacking physics and traversing across, for example, worldlines of the quantum many-worlds.
we may be able to create smaller X-risks, that only make us extinct in this timeline, on this earth. there are a few reasons we may want to do this:
smaller X-risk, where we limit damage to just our civilization, seems harder than tiling the cosmos with paperclips; but at least it might be easier than other plans.
in a similar way, reducing our civilization to ashes without actually becoming extinct might also be a way to get another shot, if we think we're likely to do less badly next time.
remember: this is bigger than all of us. when the fate of the cosmos is at play, we can't afford to be too selfish.