How severe is congestive heart failure?

Well - depends!: It all depends on exactly what you asked - how sever is it ? Its never really good - when its severe - well, then i guess you would say its 'severe' and bad. If its 'mild' - hey that doesnt seem tooo bad - but, i'll skip it if you dont mind -.

No Symptoms to Fatal: Like most issues, varies very widely. CHF typically progresses slowly over years to decades & is not recognized until symptoms become severe enough that people finally seek help (way down the road) due to shortness of breath (lung edema), leg edema, increasing fatigue, etc. Alternatively, it can be detected early, before symptomatic, in several ways; good quality echocardiography probably best.