This study investigates the areas of resilience and vulnerability in sentential negation in heritage Egyptian Arabic and explores their theoretical implications. Egyptian heritage speakers completed three narrative production tasks, five experimental production tasks, and a acceptability judgment task. The results indicate that they have a full grasp of the location of negation and its configurational properties, but diverge from native speakers in such aspects of sentential negation as merger with lexical heads and dependency or licensing relations. We propose that these asymmetric patterns are due to various factors, including the age at which a structure is typically acquired in the L1, as well as its morphological and syntactic characteristics. The results of this study have implications for the ongoing debate in heritage language research about the linguistic areas that display greater stability/vulnerability. For example, phrase structure seems less vulnerable than licensing dependencies and the mapping between syntax and the morphological interface.