I guess the keyword is "where reasonable". With non-certified engines, it's plain illegal to fly over terrain without emergency options, because an engine failure is a non-event by their standards.
With a certified single engine, you can do that if there no other ways, and if I crash due to an engine failure in-flight, the engine manufacturer and the maintenance guys will be investigated too. Not that it makes any of the pain lower, but this puts pressure on both to do a good job, use quality materials, tools, testing equipment etc.