Speaking of unpredictables, JK Rowling is a mistress when it comes to that. The ending events in all books had us expecting the unexpected.
Like in Sorcerer's Stone wherein (SPOILER)Quirell found the Mirror of Erised.
In Chamber of Secrets when it was actually (SPOILER)Ginny who opened it.
In Prisoner of Azkaban when we found out that Sirius Black was actually (SPOILER)Harry's godfather.
Goblet of Fire reveals it was (SPOILER)Crouch Jr. who sent the Dark Mark and disguised as Mad-Eye Moody.
In Order of the Phoenix, (SPOILER)Sirius dies and the Wizarding community finally knows about Voldemort.
The Half-Blood Prince turned out to be (SPOILER)Severus Snape.
With all those heart attacks, I'm bound to expect MORE from Deathly Hallows.