If the enchanted creature leaves the battlefield in response to the triggered ability but the Aura is still on the battlefield, the Aura will be put into its owner's graveyard as a state-based action. In that case, the last time it was on the battlefield, it wasn't enchanting a permanent, and its controller will not draw a card.

Historian's Wisdom has an intervening "if" clause in its triggered ability. This means that you will draw a card only if the enchanted permanent is a creature with the greatest power both at the time the ability triggers and at the time that it resolves.