This isn't something they are going to agree on. Kairi believes his world is kinder than it is in truth. Thanatos doesn't want to lie to her, but they will just go in circles like this if they continue.

"Perhaps. There is only one way to know for sure." Mort nuzzles his cheek, offering his support. "I know you have others to say goodbye to, so I won't keep you. Still, you'll take care, right?"