Can leg claudication ever get worse on its own?

Certainly. Claudication describes the symptoms of muscle cramping and/or foot numbness/pain with exercise. People with mild to moderate vascular disease experience claudication. It is very possible for the vascular disease to progress to severe disease, in which case people develop rest pain or tissue loss. Smoking cessation, Aspirin and a cholesterol lowering medication (statin) will help.
Yes. Clarification as with any form of peripheral vascular disease is progressive. If your symptoms have worsened the you should see your vascular surgeon.