There are several synonyms for the phrase "falls back on." One such word is "resorts to," which suggests a sense of desperation or last option. Another synonym is "reverts to," which implies returning to a previous state or behavior. "Depends on" is another possible synonym, indicating reliance on a particular course of action or resource. "Relies on" and "falls back upon" are also synonyms, both indicating a reliance on something or someone for support. In essence, all of these terms convey a similar idea -- that the individual is relying on a particular resource or behavior in a time of need or uncertainty.