The material in a CS degree is pretty accessible for self study compared to that of some other majors. No expensive materials are required beyond a $500 computer. Instructors don't generally spend time with you while you are actually programming, so you won't be missing the kind of 1 on 1 feedback a music major would get. Also of critical importance, CS materials tend to be strongly represented in MOOCs. There are already people using Coursera, edX and OCW to complete full degrees (see: http://youtu.be/piSLobJfZ3c).
As far as credentials go, it's a similar story. There are few fields in which the credential matters less than they do in tech jobs. Tons of my friends work at YC companies with either unrelated degrees or none at all. I personally graduated with a Japanese degree and still managed to break into the industry quickly once I started focusing on developing my hard skills. I received interview offers from pretty much every top tech company in the bay area and the degree never came up. I very, very nearly took one of them but instead chose to do a start-up. At this point it's possible some investor would be hesitant about us because we don't CS degrees, but it's also probably likely they'd be interested in our exceptional backgrounds.
One caveat to this is is that without the CS degree you have to have the skills. Also I wouldn't count too much on being an iOS domain expert since specific tech stacks keep changing. You probably want to learn all the things you'd get from a CS degree if you don't have them already.
Unlike a lot of posters here I really don't see anything wrong with not getting the degree. I would strongly suggest that you make a bargain with yourself and save/invest everything you would have spent on college. That will limit your downside and give you the option to stop working and get the degree if you change your mind and/or find your skill-set is no longer in demand. Even if you learn the equivalent of a CS degree on your own, you might find yourself wanting to return and study something like applied math, which pretty much gets you by the credential barrier for any job a CS degree does plus quite a few others.