Partisans didn't win control over Yugoslavia either, they had their "free territory" that shrunk and grew, mostly in relation to whether Germans were actually doing something against partisans at the time. So in '44. Red Army swept trough, helped liberate most of Serbia and continued north trough Hungary and Austria, with partisans slowly liberating rest of country during the following year.
So Chetniks couldn't "win control over Yugoslavia" any more than that. They could become the stronger and more successful resistance movement than partisans (trough ASB help most likely), but it would be very difficult for them to completely destroy Partisan movement, so when Red Army comes for a polight visit in '44...
Sure, IF they marginalized Partisans, and IF they managed to get Allies to land on Adriatic coast before Red Army came ever close to the YU borders... and a couple of similar far stretch IFs... than they could have done it and there would likely be restoration of monarchy after the war. With events of war and such post war Kingdom of Yugoslavia wouldn't be any more democratic than Greece untill the Colonel's rule ended, maybe even comparable to Franco's Spain. In NATO sure, if Churchil managed to convince Stalin to accept a fully western Yugoslavia.