Shel,
I'm not sure someone's happiness dependends on being able to hear but I think instead, it depends on the person and what they have experienced in life. I'd also have to say if someone was hearing and lost their hearing over time then maybe they would be unhappy in that their life has changed considerably from what they knew. This may also be different for someone who lost their hearing slowly as compared to someone who lost it very quickly. Maybe with some, it would be like loosing a friend really close to them (parent, spouse, child). For me, I had the option of getting a CI and it is working really well and I know I am fortunate. Because this was an option while I was loosing my hearing, I did not go through the mental and physical loss.
For my quality of life improving with a CI, I don't think it has taken away from my life. I do think that if I couldn't hear then it would affect the responsibilities I have at work and how I communicate with other co-workers if they would even be willing to try and communicate with me.
I was thinking over the weekend and wondering how someone who has been deaf their entire life would respond to hearing sounds. I think understanding speech would be the hardest part. The best way I can think of it would be for me to try and listen to a foreign language and try to learn how to understand it and speak it. This really got me thinking especially because my ability to hear sounds has changed as the healing process takes place so what I heard the 1st week is different than what I am hearing today. I could see where this could be a challenge for someone not familiar with sounds.
Understanding environmental noises I think would be easier since for the most part, many sounds are the same from place to place but with speech, there are so many different accents and ways to express ones thoughts.
I know this doesn't answer all your questions or thoughts but maybe it is like someone who is single and getting older but has not found the right person to settle down with while all their friends were getting married and starting families. I know I felt this way for a while, it just took a little longer for me to find the right person but I did feel at times "empty". Not the right word but hopefully you get the idea. Maybe this makes sence.