"Critical engine" is a relative condition. If the Vmca difference is only a knot or two, it hardly pays to have the expense of two different engines.
And the reason turbofans aren't LH/RH is because of the stator vanes behind the fan rotor. Without them (like in a conventional propeller) the downstream airflow is a vortex about the prop/fan axis. The stator vanes recover that vortex energy, and create a linear airflow field. So it makes no difference if the fan rotor turns LH or RH.