Why did Darth Vader decide to kill Ashoka no in Star Wars Rebels when she said won't leave you?

Answer 1

First, Ahsoka didn't die. If you watch that episode again and go to the part when Vader limped out of the ruined temple, after the bird soars overhead, if you look very closely, you can actually see the back of Ahsoka walking back into the temple. It was hard for me to spot at first. Second, Vader wanted to kill her because she's a living reminder of who he once was and wants to eliminate all ties to his past.