Hold up, were forgetting that massive explosion the 2 were in the center of? Who's to say that didn't end it? Vader makes sense as being alive, due to his armor and that he's been at the center of large explosions only to emerge rather unharmed if not a little damaged.
So....the explosion could have also ended the fight and her.
But just a thought really given the size of it, but guess we just gotta wait for confirmation.
__________________ "We are the rage of the Warriors of the Shadow! The first noble sons of Mandalore!"
―Excerpt from the traditional Dha Werda Verda chant
What? If anything Filoni's interview confirms that she is alive.
"I would just say that there are probably – and I’ll give you this as we go back a ways – there are probably more stories to tell with Ahsoka Tano, but I would not believe that that would happen necessarily on Star Wars Rebels. I’ve been wrong in the past, but I think that she has served the part of the story that she needed to for our characters here."
He says he's been wrong in the past meaning its fully possible that she'll return even in Rebels. And as I said Filoni drew heavily on The Fellowship of the Ring's Gandalf the Grey in this series. And I think that Ahsoka will come back, she'll come back different, but she will come back.
Then again 'an image of the back of Ahsoka Tano' seems terrible.