His Tender Mercies by EnigmaticBlue
Wolfram & Hart make a slight error, and bring Drusilla back instead of Darla at the end of AtS S1. Drusilla heads straight to Sunnydale and Spike, and in the process throws a monkey wrench into Buffy's thinking.Miranda's
Soulmates has a sane-ish Dru in the end. Her site disappeared years ago, so someone else might have a link. I have a text copy.
there's a few with Dru becoming sane...r, but not quite within your brief. Dee Bradfield's
Shades of Grey series for instance. Dru's sanity is sort of restored in the end