Albus Dumbledore retired from teaching to run the Northern Scotland Wizarding Childrens Community Theater. He directed an exceptionally horrible production of Shakespeare's "The Tempest" and has not been heard from since.
Minerva McGonagall took over the position of Hogwarts Headmistress and added "So You've Decided To Illegally Become An Animagus" to the required reading list for all fifth-year students.
Severus Snape left Hogwarts following a scandal around allegations of an inapropriate relationship with a student. He was cleared of all charges and currently works for Weasleys' Wizarding Wheezes extracting and refining Doxy venom.
Fred and George Weasley married a pair of American muggle twins in a double ceremony (on April 1) They currently have five children between them. Weasleys' Wizarding Wheezes is now the largest supplier of wizarding novelties in the world.
Vernon, Petunia, and Dudley Dursley were quite happy to finally be rid of "all this magic nonsense" and have settled down to a more proper muggle lifestyle.
Neville Longbottom went straight from Hogwarts into the Auror training program. He is currently on the fast track to becoming head of the Magical Law Enforcement department of the Ministry of Magic. His grandmother is still saying he doesn't measure up to his parents.
Ronald Weasley never quite made it out from the enormous shadow cast by his various siblings. He now plays Keeper for the Salt Lake City Seagulls and is leading them to the first championship in the history of the team.
After the Triwizard Cup incident, Percy Weasley couldn't get arrested in wizarding Europe. He currently lives in New Zealand. The git.
Sirius Black is still dead.
Hermione Granger became the youngest Minister of Magic in history at age 21. Her non-human rights platform was an express elevator to the top. She was unceremoniously sacked two months later, when her House-Elf Liberation Decree "flooded rooftops and rail crossings" with suicidal house-elves.
Ginny Weasley went on to be a Chaser for the Holyhead Harpies and tops the shortlist to be on this year's English National team.
Draco Malfoy fled to the United States to avoid prosecution. He has since returned to his criminal ways and now shares a cell with a Troll who thinks he has "A purty mouth."
Harry Potter made the ultimate sacrifice in his defeat of Lord Voldemort. He currently lives in northern Saskatchewan with his wife Millicent and their 15 children.