I have found that if SDL_mixer.dll is missing from a system, even if it is never referenced, on application close the system will crash due to a call to CloseMixer().
I think that CloseMixer() in Events.cs should be changed to:
public static void CloseMixer()
if (Sdl.SDL_WasInit(Sdl.SDL_INIT_AUDIO) != 0)
// No DLL? No problem.