I think we can assume we'll see Missy again. She was pretty great once she was able to start just acting like herself rather than as someone else. Insightful glimpse into the mind of a madman, too. He still just wants her best friend in the whole wide world back.
Too bad she lied in the end, but what's to bet it really is right there and the Doctor somehow missed it?
Overall, I quite liked it. Another love-conquers-all story, but I'm okay with it. Danny Pink is a good man. The Doctor isn't a good man, and I hope he manages to hold on to that realisation for next season.
And dat ending cameo. Nick Frost is the best.