The first and least likely is that Assads Alawite army changes side, why would they commit suecide? Second event to change the situation is hundred of thousands of refugees fleeing into Turkey, this senario is the most likely to bring about a change infavor of the opposition. The third and last senario is the outbreak of war between Syria and Israel, but unlikely to happen soon and in the meanwhile the revolt could have been crushed.
Australian police arrest 5 over shooting 'linked to terrorism' (Reuters)
from the article: Syria security forces kill 10 at Friday protests