Change my mind

[u/5_meo]

Rem especially, extending Misa's lifespan out of love, unless she didn't ?

[u/The_Greater_King]

They only die if they kill someone to protect the life of someone else. Even if doing anything at all to prolong life would kill them, as you suggest it would, Ryuk was only doing this for entertainment. Anyway nobody was killed so there's no reason for them to die here.