I got a 8cm ovary cyst from pregnancy but then had a miscarriage is it likely my cyst would shrink away as there's no pregnancy anymore. ?

Sometimes: Sometimes large ovarian cysts like yours will resolve on their own. Other times the gynecologist needs to remove them. If you are having symptoms from it your gynecologist can monitor it with ultrasound and you can make the decision with the doctor about treatment. Often this removal can be done with a scope, not requiring a big surgery.

Yes: The cyst should shrink back down, but 8cm is a very large cyst and bears watching. Hope this helps. Best of luck.