The 737 classic (which the incident aircraft is) uses hydro-mechanical controls. It can be flown with zero functioning electrical buses. The only electric part

The 737 classic (which the incident aircraft is) uses hydro-mechanical controls. It can be flown with zero functioning electrical buses. The only electric parts of the primary control system are the electrically-driven auxiliary (backup) hydraulic pumps, the stick shaker (stall warning), and the motor for pitch trim (located in the cockpit, connected to the trim wheel). Unlike the MAX, the classics have a large pitch trim wheel with lots of leverage, so you really can fly it with manual trim. In the event of a full hydraulic failure, the ailerons can be operated mechanically from either seat, and pitch can be controlled via the elevator trim mentioned above.