Another clue on Sirius' possible return:
On Harry's first night at Grimmauld Place, the entire house sits down to dinner. In total, 13 of them eat together.
According to Trelawney in PoA -- "When 13 people dine together, the first one to rise is the first to die."
"Sirius started to rise from his chair." -- but he only half rose from his chair -- so could this mean that he is only half dead?
just one more (sad) note though -- the one to fully rise up from that table was... Ginny! to play with the cat!... but i suppose that this clue no longer applies to her since Sirius is indeed the first to rise -- even if he only "half-rose up" from his chair..