"would be fine if i died right now" mean "i love u too" but hina can"t get it :))
Actually Hina get it but played it cool. When Sayo look at her, her ear turned red. And the best thing is Sayo realized that. That's why Sayo smiled and said Hina do change after all. Both do realize they're saying "I love you" to each other. Adorable!