I've been avoiding answering this question for a couple of days because I wasn't directly involved with the situation I'll relate to you in a moment, and I wanted to see if you got any responses that were better than mine first. But you haven't so I thought I'd go ahead and throw in my two cents.
One of my nephews was diagnosed with torticollis when he was about six months old. I know the anxiety that my sister-in-law had with the whole situation and the guilt that she had because she always seemed to feel like she wasn't doing enough to remedy the situation. They tried turning his head when he was sleeping and ensuring that he had lots of tummy time, but it didn't seem to help. So, ultimately, he had to wear a helmet.
He's 4 1/2 now and I can't tell any kind of impairment or difference between him and his cousins (there are seven cousins between the ages of 1 year and 5 years...it's pretty easy to compare them to each other when it comes to basic milestones). I'm pretty sure he wore the helmet almost constantly for about six months or so (could have been longer, I'm honestly not 100% sure). From what I understand, the helmet was pretty light-weight and he got used to it pretty quickly. I think he also had additional physical therapy to strengthen the muscles in his neck and encourage him to turn his head in the other direction. He's a normal, healthy 4 year old now and he hasn't worn the helmet in years.