Emissary of the Sleepless’s last ability checks only if a creature died earlier in the turn. The creature card doesn’t need to still be in the graveyard.

Token creatures that are destroyed or put into a graveyard from the battlefield for other reasons do die—they go to their owner’s graveyard before ceasing to exist.

Emissary of the Sleepless’s last ability doesn’t create additional Spirit tokens if more than one creature died this turn.