Microstructured falling-film reactors have demonstrated their relevance for fast and exothermal gas-liquid reactions. Microstructuring enables to stabilize gravity-driven films and to operate with thin films at low flow rates. Unfortunately, the surface of the separating walls remains dry. For plasma-activated reactions, dry patches may create short-circuits and should be avoided: the liquid film should overflow from the channels and wet the whole surface. This film overflow is explored via experimental measurements and a numerical energetic analysis. A set-up was designed to visualize the film flow with liquids that exhibit various contact angles, enabling to draw flow maps of the stability domain. These results have been compared to a set of CFD simulations for varying flow rates and contact angles: 24 geometries have been designed to consider various positions of the gas liquid interface, and 78 3D simulations have been performed by combining these geometries and appropriate fluid properties. They enabled to draw numerical flow maps to be compared with experimental maps. This comparison yielded to a good agreement with particularly interesting trends confirmed by geometric considerations. By including energetic aspects related to the various surface energies involved, the frontiers of the numerical flow map confirmed the experimental measurements.