The phrase "fell through" generally means that something that was planned or hoped for did not materialize as expected. However, there are some words or phrases that can be used instead of "fell through" to express a similar sentiment. "Failed to materialize", "disintegrated", "collapsed", "went awry", "disappeared into thin air", "vanished", "came to naught", "ended in disappointment", and "did not come to pass" are some examples of synonyms for "fell through". These words or phrases can be used depending on the context and the level of formality required.