Recent work has demonstrated that it is possible to generate frequency combs in normal dispersion microresonators by taking advantage of fabricated mode coupling that induces a mode split. In particular, photonic crystal resonators periodically modulate the microresonator's width, which geometrically creates mode coupling. In contrast to frequency combs generated by microresonators in the anomalous dispersion regime, which are typically generated using bright solitons, the frequency combs generated by normal dispersion regime microresonators are dark pulses that are commonly referred to as dark solitons or platicons. In this work, we examine the linear stability of platicons in the pump-detuning and pump-power parameter space as the mode split strength and cavity dispersion is varied. Our work reveals a broad region of stability for platicons. Our work also reveals the existence of fingers at high power at whose boundaries a sharp transition occurs and inside of which platicon solutions are bistable. Finally, we investigate the overlap of the region where platicons are stable with the region where continuous waves are modulationally unstable, and it is possible for a platicon to self-start. Simulations show that platicons consistently self-start inside this region.