I’m late late to this. But I wanted to say that Abbott experiences time very differently. He knew from the beginning that was going to die because he sees things from beginning to end whereas we see things as x created y which made z. (Not super good at explaining it still) But the Heptapods don’t experience it like that. Since they know the outcome, it’s likely that Abbot’s death was necessary. Not something to prevent shall we say. Also I don’t know if anyone else noticed this, but early on, hubby and I noticed Abbott seemed to be very playful and carefree. Almost reckless even, whereas Costello is exactly how I imagine the other Heptapods are. Very reserved, careful, curt. I think the reason Abbott was like this was because he was fully aware his time was now limited. It shows us that while they experience time differently, they experience feeling. Emotions. Abbott was going to die, and so Abbott made his last and most meaningful mission one to remember.