Effort to hide, or too launch? Though both wouldn't be for us but from anything that they have to assume behaves similar as them, at some point. How likely is that this would be any significant effort for them at all?

But I also believe that the stance is unlikely and they hopefully had more caring thoughts for us... like we care for all the extinction of our fellow species on this planet.. ehm or maybe should, but they taste too good and I need my house warm :D

So, what about the cleanup effort?

Let's say you're a civilization advanced enough to direct world-destroying missiles at everything 100 LY around you... that means you can reasonably get some intelligence on what you're destroying, and it's probably valuable enough territory to make it worth checking out before you incinerate it. A 100-year mission to go there and, oh, alter the atmosphere just enough to eradicate the dominant species, would be a much better strategy than just annihilating a productive ecosystem...