Voldemort still killed David Monroe, he just did it earlier than everyone thought he did. Chapter 108:

I had long ago taken my vengeance on David Monroe - he was an annoyance from my year in Slytherin - so I bethought to also steal his identity, and wipe out his family to make myself heir of his House.

Your other questions remain, though. Harry no longer killed Voldemort for good, and Hermione (apparently) has. This should be interesting. I predict this becomes an issue, confidence 70%; and, conditional on that, that Draco sides with Hermione again at a crucial moment, confidence 85%.