So here’s what happened in 6th year: After the episode in the ministry in their 5th year, Lucius and the other death eaters present made their escape and were never imprisoned.
Draco wasn’t up to something. But his father was. He was the one to break in to the school and the one who killed Dumbledore in the Astronomy Tower. He did not bring any death eaters, and hence no students or professors were harmed.
Seeing as the last Horcrux was destroyed by Dumbledore and Harry no Horcrux hunt during 7th year was necessary and all students attend school as planned.
Harry is dating Ginny but she is acting increasingly strange. At the same time Harry befriends Draco Malfoy, much to Ginny's annoyance and his own surprise.
Lots of drinking games and randy teenagers.