Why don't you connect unused hot and neutral wires to "complete the circuit"?
You don't need to "complete the circuit".  Tying together the hot and neutral wires creates a short circuit, which should immediately trip the circuit breaker.  If you're removing a vent hood, you should put a wire nut on the end of each now-unused wire (to prevent a short circuit) and close up the box.

Every unused outlet in the house is an "incomplete circuit".  Presumably you don't install jumper wires across each outlet every time you unplug something, right?