As soon as Inferno Fist leaves the battlefield, its power bonus stops applying. This means that if you sacrifice Inferno Fist before combat damage is dealt, perhaps to destroy a potential blocker, the creature that was enchanted won't have the bonus when it deals combat damage.

If another player gains control of the enchanted creature, or if Inferno Fist becomes attached to a creature another player controls, Inferno Fist will be put into its owner's graveyard as a state-based action.