My best friend's horse had colic surgery and he was only about 3 years old at the time. She had him insured so the insurance covered all of it. I think it was around $10,000.
I already know that as much as I love my guys, colic surgery is something they won't have done. I will do as much as I can without surgery, but I can't afford any $10,000 vet bills. I had two horses put to sleep due to colic, but they were already in their 20's. Not that they were loved any less, because they were loved greatly, but I think if a 25yr old needs colic surgery, I think I would opt to put them down rather than put them through that at near what is the end of their life. But if it comes right down to it, the young one would get put down too if it came to that. So I pray it never does.
However, the good news is, my friends horse recovered just fine and is still out hitting the trails for 5 hours at a time. He seems totally normal. I think he had some infection at the surgery site, and for about a year afterwards he would have an occasional colic episode, but at the moment he is totally healthy and has recovered great (it's been about 2 years now).
So if you can afford it, yes, they can definitely go on to be normal and have a good quality of life.
I don't think they ever figured out exactly what was wrong with my friend's horse. Part of his intestine (many feet of it, I don't remember how many) were removed because it didn't look healthy, but they never did figure out what caused him to colic to begin with.