This can be stated in active form. The word "hand" is a metonym for the power of the owner of the hand. Possible meanings are 1) "only if he sees that he has no power to do anything else," where the "hand" belongs to Pharaoh; where the "hand" belongs to Yahweh, 2) "only if I force him to let you go" or 3) "not even if I force him to let you go." (See: [[rc://en/ta/man/translate/figs-metonymy]] and [[rc://en/ta/man/translate/figs-idiom]] and [[rc://en/ta/man/translate/figs-activepassive]])
The word here "empty-handed" is used to emphasize the opposite meaning. AT: "will go with your hands full of good things" or "will go with many valuable things" (See: [[rc://en/ta/man/translate/figs-doublenegatives]])