My filling fell out months ago and I never had a chance to get it filled back. Is it possible the teeth might fall out?

Not likely. Teeth fall out generally for one of two reasons. 1) a baby tooth where the root has been resorbed. 2) severe bone loss from many years of neglecting gum & bone disease (periodontal disease). As the decay gets worse, you may need a root canal and crown or if to severe, the tooth may need to be extracted. You need to see a dentist asap before a severe infection develops.
Unlikely, but....... I doubt your tooth will actually fall out. This usually occurs with years and years of periodontal neglect and destruction of bone from periodontal disease. It is more likely that you will need root canal therapy and\or a crown if you wait too long or if there is already extensive caries. Even worse would be the need to have the tooth extracted if it is un-repairable. See a dentist asap!