For me, it remains to be seen.
Last year I got a period that lasted 5-6 weeks and ended up at the OB/GYN's. I was only ~117 pounds at 5'4" and didn't have much hair in the wrong spots. But my fasting insulin was. . .21 something-or-other, if I recall correctly. One or both ovaries was 150% normal size. I had 8+ cysts in each ovary. And at 27, I'd never had regular periods aside from maybe a 3-month span early into puberty; by 27 they were about 1-3 a year.
I took less than one month's supply of metformin (which really made me feel sick). And only one round of birth control pills. And I kept reading up, furiously scouring for any hope of stopping insulin resistance and PCOS, and landed on Dr. Barnard's work on reversing diabetes on a low fat, low GI, vegan diet.
I tried a few supplements I didn't maintain for more than a few months, finding I got a period shortly after beginning Vitex (started V June 21st, got P on July 8th) but getting worried when another didn't soon follow. Added in vitamins known to help insulin sensitivity, which I still take occasionally (mainly to help me sleep). Around this time I began cutting the fat out and not eating many animal products. And exercised 30-60 minutes most days (trying not to be too strenuous because i read that could be counterproductive. . . by increasing testosterone, was it?) until I pretty much stopped with winter weather. After my period on July 8th, l had to wait Sept. 11th (by which point I was taking d-chiro-inositol) for the next. Then I started thyroid meds in mid or late October--8 years after being diagnosed with Hashimoto's. Got a period on October 27th! Late Nov, thyroid meds upped. Get my next period December 2nd (36 days from the last one!). Then a 33-day cycle. Prescribed Tirosint (a synthetic T4 thyroid med) on top of my Armour (a thyroid med from pig thyroids containing T4 and some other hormones). The next cycle was just 31 days! Then last time, I got scared. I had ate too much fat mid-cycle during a surprise birthday party for me and was afraid I'd messed things up. But I got a period on day 35!
So my period is BACK and, this late in life, better than EVER!! But I haven't done a follow-up ultrasound (which wouldn't prove PCOS is gone since cysts don't always build up, just possibly give me an idea; plus I suppose the cysts from last year might still be there--perhaps that's why the acne persists mildly?--and we wouldn't know if they were new or old). The only insulin test I've had since my insulin resistance diagnosis is proinsulin, which a Dr. thought a good insulin resistance measure. if it is, I think I'm going quite well. Range is 0-10 and I got a 1.5 (I think it was; I should pull my labs out). But I'm supposed to get a serum insulin test soon, so hopefully that shows something very good.
If that's good, I hope to take a fasting test with the glucose drink again (that's what I was diagnosed with).
I have mild acne still, not sure why, but I know it's not so bad when I follow my low fat diet better. I use stuff from Amazon by Acne.org to help it. My four dots of cystic(?) acne from last year are still down in my skin, though. My hair needs washed the night before a given day, at the earliest. And I thought at one point recently my testosterone might be worse, though I still have very mild male-pattern hair (like I used to go months between shaving the very light, soft, thin hair in the sideburn area). It tested at the very top of the range this winter (Dr. who ran the test at my request thought the range was general, oddly not listing one range for females and another for males. . . if so, YIKES!). But I am sure I am improved some. I have a lot more energy and don't seem to crash after meals (well, except when I ate white potatoes recently. . but maybe that was just too close to my fatty birthday party?); it's not just thyroid meds, as it depends on how I eat. And I am generally less pouchy in the stomach. (I am fatter, oddly. But I also am trying to stay fatter. And who knows for sure what role gaining weight had in helping my periods, though they weren't regular when I used to be this weight....)
I am now starting Taking Charge of Your Fertility
by Toni Weschler, recommended by a woman here. With the help of the fertility awareness method it promotes, I hope to REALLY know what's going on in my body. And I'm still trying to figure out how to lower testosterone naturally (cut out the onions and garlic? take supplements?...). And I am going to look a bit more into using progesterone (the bioidentical, transdermal form Dr. John Lee recommends; or shots) to see if that might be a good way to go, if needed, to get rid of any cysts I may still have. (I'm hesitant because Dr. Lee talked about the cream training the body's progesterone levels; and now that I have my periods, I'm even less convinced I want to try messing with hormone levels.)
Try looking up posts on PCOS by Ms. Doodlepunk. She was in a metformin study years ago and found her insulin levels were much higher on metformin than they have been since on the McDougall diet (even eating white[?] potatoes!).