Like it says on the tin, I'm looking for Lost and Broken Things by poppymoon3. Summary: Sam says no, and keeps saying no.  Lucifer reverts to plan B; Sam, the descendant of an angelic line, tainted by demon blood, is the ideal vessel for the creation of a special child...(mpreg Sam)

It would have been completed in mid-2010 and been 15 parts.

Both Google cache and the Wayback Machine have nothing. On the Deleted Authors page here, the author didn't prohibit sharing their works, so I'm hoping someone made a copy of it.

Found by meus_venator! Link in comments.