Has JKR killed off any characters outside of book/movie canon?

Question

A lot of beloved characters were killed off in Deathly Hallows; there were literally corpses lined up in the Great Hall. However, there are a lot more characters in the Harry Potter world whose ultimate fate was not explored, at least not in the books or movies.

What I'm asking, then, is if JK Rowling ever retroactively killed off any more characters after publishing Deathly Hallows. For instance, in interviews or on Pottermore.

Some qualifications:

• If they died in the movies but not the books, they don't count (so not Lavender).
• If they were not seen alive (and not in flashbacks/magic mirrors) in the books or movies, they don't count (so not, for instance, Harry's grandparents).
• Time of death should be between Harry's birth and the epilogue of Deathly Hallows (so not 'everyone dies eventually').
• Works by other writers (Cursed Child, etc.) do not count.

Answer 1

Nicholas Flamel

Rumor: Nicolas Flamel is going to come to Hogwarts to teach potions

Flamel has now died; Dumbledore explained in ‘Philosopher’s Stone’ that his old friend was going to choose death rather than allow his stone to fall into the wrong hands.

_{old jkrowling.com - Rumors}

While it make look like Dumbledore made this clear in the books, Rowling would later very emphatically declare on Twitter that it was never in the books. (So I guess WoG says that this was a death not in the books?)

Kreacher

What happened to kreacher, the house elf after the books?
JK Rowling: He died, aged 666.

_Twitter

Note that this one was probably a joke, considering her previous tweet and the fact that House-elves only have an average life expectancy of 200 years.

Honorable mention: Professor McGonagall

MV: Okay. Number one, 19 years later, who's the headmaster at Hogwarts?
JKR: Well, it would be someone new. Erm, McGonagall was really getting on a bit. So someone completely new. But if I ever do the encyclopedia, I'm promising I will give details.
_{J.K. Rowling One-on-One with the Today Show (NBC), July 2007}

"Really getting on a bit" doesn't equal dying, but it implies that she was going to soon.