I've always had long straight hair, until recently - went to a new-to-me hair salon and the stylist kind of wrecked my hair by chopping too many layers into it, and my solution has been to shorten up the length while also waiting for those layers to grow out.
Guess what? The collar-bone length works quite well - and I happen to have a bit of a double chin from years of being significantly overweight and then losing most of it. Still have that bit of double chin, and I can honestly say that having hair somewhere between the jawline and collarbones actually serves to make my neck look longer and my face look thinner.
Meanwhile, if you have fairly long-ish hair to begin with, this probably means your hair grows pretty fast, so if I were you - I'd have no hesitation in chopping it to collar-bone length. And yes, I can easily still put my hair into a pony tail without trouble at all. I would say that the shortest layers in the front of my face are about an inch and a half below my jaw line. No problem with pony tails. Having said that - even if some of the front layers were still too short to tie back, you can always use a bit of hair gel or spray to get the shortest pieces to stay in place.
If I were you, I'd go for it - because collar-bone length hair is still long-ish, and if you have long hair in the first place, it will grow back very quickly if you didn't like the new length.