When we talk about "passes Rubicon", we usually refer to a critical decision that has been made that cannot be undone. However, there are several different ways to express this same idea. For instance, someone who has "burned their bridges" has taken actions that make them unable to retreat. Another common synonym is "crossing the point of no return". Once this point is crossed, there is no going back. Another phrase that describes a similar situation is "leaping into the fray". This phrase emphasizes the idea that the person is jumping into a difficult or dangerous situation where there is no turning back.