Layered boron compounds have attracted significant interest in applications from energy storage to electronic materials to device applications, owing in part to a diversity of surface properties tied to specific arrangements of boron atoms. Here, first-principles calculations coupled with global optimization are performed to explore the energy land scape for surface atomic configurations of MgB2, a prototypical layered metal diboride. We demonstrate, that contrary to previous assumptions, multiple reconstructions are thermodynamically preferred and kinetically accessible within the exposed B surfaces in MgB2, and other layered metal diborides. Such a dynamic environment and intrinsic disordering of the B surface atoms in metal borides presents new opportunities to realize a diverse set of 2D boron structures. We validated the predicted dynamic surface disordering by characterizing exfoliated boron-terminated MgB2 nanosheets. Application-relevant implications are discussed, with a particular view towards understanding the impact of boron surface heterogeneity on hydrogen storage performance.