Being dead and walking live into the realm of the dead aren't always the same thing, though... (Despite the veil. Heh.)

But like I said, this theory doesn't quite feel right. It's also been pointed out that Harry has in fact 'descended into the Underworld' several times throughout the series, in a figurative sense, and that may just continue.

(When was this interview about not killing Sirius, anyway? I never heard that one when people were speculating on the OotP "big death." D'you know where I could read a transcript?)