A token creature that’s destroyed is put into its owner’s graveyard, and will be counted by Hellfire’s effect. (Immediately after Hellfire finishes resolving, the token will cease to exist.)

Hellfire checks the number of creatures put into graveyards as the result of its effect, not the number of creatures destroyed as a result of its effect. For example, a replacement effect that says “If a creature would be put into a graveyard from the battlefield, exile it instead” won’t affect whether a creature is destroyed or not, but will affect whether it’s put into a graveyard or not.

A creature that regenerates instead of being destroyed doesn’t leave the battlefield, so it’s not put into a graveyard.