Heh, yeah, another one of these. I read this story a while ago, so I'm a little fuzzy on the details (it even might have been an nfic, but I don't remember).
Anyway, there was another asteroid like Nightfall headed to Earth, only this time Lois and Clark are married and have kids. Clark has to go even though it's pretty much a suicide mission. They take a vacation (up in the mountains, I think), and just spend time together as a family before he leaves.
Hope that was enough detail, I don't want to ruin the end for anyone who might be interested :p
Thanks for any help,
Jessi