In an excerpt from her Today show interview (to be aired Thursday and Friday this week) JKR said she is intending to write that tell-all encyclopedia--yeah!!! She emphasized that it won't be right away, but hey, I'll take what I can get.
She also gave away which character got the reprieve. I was right about half of it--I thought Hagrid got the reprieve and Tonks and Lupin died in his stead, turns out Mr. Weasley was scheduled to be offed in Book 5 (not Hagrid) but Tonks and Lupin were the ones to take his place. I knew one of the Weasley's had to die, but I'm really glad it wasn't Arthur--what would we have done without his jokes about plugs and finding out how airplanes stay up?