A combinatorial Gauss-Bonnet theorem is proved by B. Chen in THE GAUSS-BONNET FORMULA OF POLYTOPAL MANIFOLDS AND THE CHARACTERIZATION OF EMBEDDED GRAPHS WITH NONNEGATIVE CURVATURE (P. AMS, 2009), but previous work in the same vein was done by Schlafli and Poincare. More recently also by this same Bienfang Chen.
For Myers-Bonnet, see this preprint by Saucan