The role played by single-atom vacancies on the electronic properties of in-plane heterostructures composed of graphene islands and hexagonal boron-nitride sheets is studied in the framework DFT calculations. Our findings show that boron monovacancy does not induce any nitrogen-nitrogen reconstruction whereas the carbon one induces a pentagonal reorganization for the carbon-carbon bonds. The removal of a nitrogen atom can yield a boron-boron reconstruction. However, such a bond arrangement does not take place in some cases suggesting that the relative mixing of carbon islands in hBN sheets improves the stability of boron-boron bonds.