If this happens, it would mean the ACA exchange market would drop by more than 1/3 from the ~24.2 million currently enrolled (myself & my own family included).
However, I've repeatedly stated that even this is likely a low estimate--the remaining ~16 million exchange enrollees would still be hit with MASSIVE (and in some cases eye-poppingly huge) premium hikes which would force them to drop to far worse plans (meaning much higher deductibles & co-pays; worse provider networks and so on).