There were several questions in the OP.
Rapid weight loss such as 50 pounds in 6 months will likely reduce the breast mass, but not nearly as much as you hope for. The breast area is one of the first places where we deposit fat and seems to be the last place where it is lost. In some cases, weight loss even to an unhealthy degree fails to diminish the breast size significantly.
We have heard from body builders who tell us that when the breast tissue is perched upon an otherwise well defined pectoral muscle it can Be even more evident.
Surgery. You are not alone in your fears, but they are based upon some very old data. Modern surgery by a well qualified surgeon is quite safe. You could lose more blood from a minor cut on your finger than you are likely to lose in the operating room. The Emergency Room can be a chaotic and bloody place, but an operating room is calm, controlled and nearly bloodless.
Is there another way to get rid of it? Well lets see, Do you believe in the Easter Bunny, the Tooth Fairy, etc.? "Cures" for gynecomastia are kind of like them. We'd like to believe it was possible, but we really know better. There are a lot of schemers who are more than glad to prey upon those who have more hope than good sense.
Is cosmetic surgery just for those who are vain or self possessed? This is simply another myth that refuses to die. If you had a very large, discolored, ugly, but benign growth on the end of your nose, would it be vanity to have it removed? Of course not. While Gynecomastia may not be as obvious as a facial growth, I think there is a valid comparison. It is not necessarily vain to wish to look your best.