Yes, it is possible for a microwave to be partially broken, including the magnetron, and still heat up food. The magnetron is the component responsible for generating the microwaves that heat the food. If it's damaged or malfunctioning, it may not produce microwaves at full strength or efficiency, but it can still emit some level of microwave radiation that can heat your food.
However, if the magnetron or any other critical part of the microwave is faulty, it's essential to address the issue promptly. A malfunctioning microwave can be a safety hazard. Besides, using a microwave with a damaged magnetron or other faulty components can result in uneven heating, longer cooking times, or potential damage to the microwave itself.
To ensure your safety and the proper functioning of your microwave, it's best to have it inspected and repaired by a qualified technician. Do not attempt to fix it yourself, as microwaves operate at high voltages and can be dangerous to handle without the necessary expertise and equipment.