How lethal is a congestive heart failure? My hypertrophic cardiomyopathy has turned into congestive heart failure, how dangerous is it and is it possible to keep it under control?

This. This is a very serious condition requiring close management from a skilled cardiologist, and optimally you should establish care with a large referral center with expertise in hypertrophic cardiomyopathy, such as a university hospital. Hypertrophic cardiomyopathy is not a curable condition, and when it progresses to the point that it causes congestive heart failure symptoms it is typically quite advanced and difficult to manage. There are medications that can help control the heart failure, but you should also be evaluated for advanced therapies such as a defibrillator or even a heart transplant. Your family members should also be screened for this genetic condition if they haven't already.
A spectrum. Hypertrophic cardiomyopathy includes a wide spectrum of severities as does CHF so it's impossible to comment on your specific case without much more data. In general, both conditions are potentially serious and require life long treatment. Usually people can lead normal lives with medication and/or implanted devices.