Bless your heart, you sound like you're in a dither!!
I've been reading all the responses to your initial post, and most seem positive, so I've been reluctant to post mine.
I've had several surgeries and a three level fusion. Since then, my life has been filled with unimagineable pain that I wouldn't wish on an enemy. But, for your question....
Some people have these extensive fusions and do just fine, with a little bit of limitation because of the fusing. ie: not being able to bend 'quite' like you use to, but nevertheless, are still very functional. I'm just not one of those people.
When I had my first back surgery, my surgeon made it sound like have this surgery was going to cure me, and I would be back to normal and have no more pain ever again. I was soooo nieve, but I believed him. What him and other surgeons don't tell you is the things that can happen because of having fusions....the bad hip pain, the fusion itself causing other vertebral levels to rupture because they're trying to compensate for the levels that cannot bend anymore, sciatica, problems from scarring, etc.
If you can manage to live with the level of pain that you are at now without having this fusion done, it would probably benefit you to not have it. However, you may be one of those people who have this and do fine. Sometimes, people do fine for a few months after this surgery, and then suddenly things so wrong and you end up with pain that never goes away.
It's really going to be according to you and your body, your surgeon's level of skill and how much he tries to avoid the nerves while he's doing the surgery. You may want to consider getting a 2nd orthopedic surgeons opinion, but I definately think you should see a neurosurgeon to get their opinion. A neurosurgeon is going to be very careful with the nerves that branch off the spinal canal, and nerve damage is where people end up having a lot of pain.
I wish you luck, and will keep you in my prayers.
Melissa