I don't expect Sirius to show up, since his tale was told to its conclusion. His nemesis was Peter, and Peter is dead.

Uh...

"Gosh," Harry said half a minute later, "you get a seer smashed on six slugs of Scotch and she spills all sorts of secret stuff. I mean, who'd have thought that Sirius Black and Peter Pettigrew were secretly the same person?"

and

The old wizard reached out toward another metal door, from behind which came a endless dead mutter, "I'm not serious, I'm not serious, I'm not serious..." The red-golden phoenix on his shoulder was already screaming urgently, and the old wizard was already wincing, when -

Another cry pierced the corridor, phoenix-like but not the true phoenix's call.

The wizard's head turned, looked at the blazing silver creature on his other shoulder, even as ephemeral and substanceless talons launched the spell-entity into the air.

The false phoenix flew down the corridor.

The old wizard raced off after, legs churning like a spry young man of sixty.

The true phoenix screamed once, twice, and a third time, hovering before the metal door; and then, when it became clear that its master would not return for all its calling, flew reluctantly after.