If amniotic sac is intact during vaginal delivery or c section, are chances of amniotic fluid embolisim basically zero chance?

Yes: Actually, AFE is quite a rare event and, to a degree, independent of a patient's ruptured status. The general idea is that there is a breech and/or permeability of the of the natural blood-amniotic barriers. This allows products of pregnancy to, unaturally, enter the maternal circulation and cause catatrophic events (primarily in the lungs), culminating in death, oftentimes.