Total Harry Potter freak here.
Harry will NOT end up as Headmaster, because JKR has said that none of the trio will teach at Hogwarts. There will be one student who will end up as a teacher, but it will be someone we don't expect. My money's on Neville.
I believe it was made quite clear that we won't see Sirius's spirit or ghost in Harry's conversation with Nick at the end of book 5.
Any rumors as to a release date are ridiculous, as the date won't be set until JKR hands the manuscript over to the publishers, just like what happened with OotP. And although she's said she's past the halfway mark, there's no telling when she'll be done with it.
Also, she's said it's "highly unlikely" that she'll write more HP novels past the seventh one. She says if she ever does write another book, it'll be a reference book of sorts for charity.
I don't really care WHO ends up together as long as Ron and Hermione do. Past that, JKR can do whatever she wants.
I find that JKR's official site (
https://www.jkrowling.com) and The Leaky Cauldron (
https://www.the-leaky-cauldron.org) have the best info when it comes to Harry Potter.