This study evaluates the relationship between language shift and linguistic change in multigenerational immigrant communities, focusing on North American Norwegian (NAmNo) and German heritage varieties. The research synthesizes current findings on how language shift impacts linguistic structures in moribund heritage varieties. Methods include a qualitative review of diachronic studies, comparing data from different periods to assess changes in tense morphology, language mixing, compositional definiteness, possessive placement, verb placement, argument placement, and phoneme variation. Results indicate that the last generation of heritage speakers demonstrates increased linguistic innovation and variation compared to earlier generations. Key findings show that language shift leads to different input quality and quantity, affecting grammatical stability. The study concludes that sociocultural changes, such as verticalization and domain-specific language use, significantly influence heritage language maintenance and loss. These insights contribute to understanding the dynamics of language shift and its role in heritage language change, offering valuable comparative perspectives across different immigrant communities.