I just realized something in the phrasing of Ahsoka's and Anakin's conversation towards the end.
Anakin says her name two times, and then Ahsoka says that she won't leave him this time.
Anakin then says 'then you will die'. Notice the then. It's almost like he was pleading for her to leave without saying anything, and they were so in tune with each othe Asoka picked up on that, prompting her to say she won't leave this time.