At what point should aspirin therapy for stable cardiovascular disease be discontinued in patients with a diagnosis of chronic cerebral microbleeds or possible Cerebral Amyloid Angiopathy?  

I would continue low aspirin indefinitely.

Obviously, aspirin increases the risk of bleeding so it should be stopped if possible and only be continued if there is a moderate-high risk of cardiac complications with stopping. The question of whether aspirin must be continued should be informed primarily by the patient's cardiologist.