How important is the Captain Curnow optional mission?

[nocteur]

I just finished the High Overseer mission, thinking that I had successfully kept Curnow alive... Then I get back to base and Callista tells me that he died. Apparently, I had failed without realizing it (some googling told me that leaving him in a dumpster is what I missed).

Now, I'm not sure if I should replay the entire mission to fix this. Does it have any real effect on the story or anything? I'd like to move forward with the game, but this is bugging me.

[Forerunner]

It has no impact other than callista being annoyed with you (and in the ending cinematic for low chaos he wont be there).

[OttosTheName]

Is that the guy who's toasting with the overseer?
If you save that guy you get an extra rune when you return to the Hound Pits.
So that's cool. Also you need to save everybody you can to get the Clean Hands achievement. So if you're going for achievements you should save him, but other then that... It doesn't really matter. It might count for chaos.

[Puppy Cat Underfoot]

It helps increase Callista's chances of survival.