Based upon the above said details, your father had stroke because of uncontrolled diabetic status, and you should also check for other risk factors like blood pressure,
lipid levels and cardiac and neck blood flow status, etc..
Diabetic status should be controlled and monitored properly, If there is any other risk factor, it should be also addressed..
He should be started on blood thinners and lipid lowering drugs and physiotherapy after consulting a neurologist..