What is the longest you know someone who has survived with congestive heart failure?

Too little info. Congestive heart failure (CHF) is in many ways a generic term - it is more of a symptom than a diagnosis. Someone suffering with CHF typically has shortness of breath, fatigue and fluid build up in the lung tissue. The root cause of CHF will determine the prognosis. Some causes of CHF include inherited muscle diseases (cardiomyopathy), coronary artery disease (heart attacks), kidney faliure, etc.
Many Years. I personally have many patients who have survived for many years with congestive failure. However, this disease is very serious and must be treated and monitored very frequently. Diet, fluid and weight management and proper lifestyle make a huge difference for patients with this diagnosis.
Decades. Modern treatment has changed the game completely, but requires seeing a heart failure specialist. Also strongly dependent of cause of heart failure, e.g., coronary disease, viral, hypertensive, drug induced, valvular, metabolic, inflitrative, etc., and whether there are reversible components. Need to see a physician who manages heart failure; ask your doctor to whom he would send his mother.
Depend on class . Four classes of heart failure - class i or extremely mild heart failure has very limited symptoms and if properly treated, could have normal life expectancy. Someone in class IV failure has severe symptoms and could have as high as 50% ) months mortality rate.
13 years. 13 years! well treated and closely monitored, heart failure patients can lead reasonably active and healthy lifestyles.