If there are no legal targets to choose, perhaps because all your opponents have hexproof, the ability is removed from the stack with no effect. You won’t draw a card. This is also true if the target opponent becomes an illegal target in response to the ability.

The opponent chooses whether they sacrifice a creature, pays 3 life, or allows you to draw a card. That player can’t make an impossible choice, such as sacrificing a creature while they control no creatures.