I have a dog with a terminal heart condition. He was given 1-2 years tops. I fostered him for a rescue and no one wants him because of this condition. Medication is $150.00per month...so I do understand that this is a lose lose for some. Not for me - it's a win win. He will remain with us until the end. Though the vet recommends no running, extensive walks, to be carried constantly...I have a different view on this. Let him live. Let him just be a dog and enjoy his life. He has no idea that he is terminal...so why treat him as a fragile being.
My view is just let your cat enjoy everyday as a normal day. Heart murmurs are not always so serious. One cannot figure out the lifespan of a completely healthy animal, so it would be difficult to say how long your cat with this condition could live.
It is the quality of life that is important, not quantity.
I am pleased to tell you that my permanent little foster boy has passed the one year mark. He is having a ball just being a dog without restrictions.
Your cat is absolutely stunning by the way.