I have a carotid artery blockage. If I watch my diet from now on, will the blockage go away?

Unlikely. Diet alone will most likely not make the blockage go away. Medical management with Aspirin or Plavix (clopidogrel) (anti-platelet agents) and cholesterol lowering meds (statins) will give you the best results.
No. Plaque may stabilize but will not go away. You need to control risk factors with diet, aspirin, statin therapy, high blood pressure medicine and doctor follow up with carotid ultrasounds periodically. No smoking. Check with your primary care doctor.