In a post-thermal-quench plasma, mitigated or unmitigated, the plasma power balance is mostly between collisional or Ohmic heating and plasma radiative cooling. In a plasma of atomic mixture with α labeling the atomic species, the power balance sets the plasma temperature, ion charge state distribution with i the charge number, and through the electron temperature and ion charge state distribution the parallel electric field Since the threshold electric field for runaway avalanche growth is also set by the atomic mixture, ion charge state distribution and its derived quantity, the electron density the plasma power balance between Ohmic heating and radiative cooling imposes a stringent constraint on the plasma regime for avoiding and minimizing runaways when a fusion-grade tokamak plasma is rapidly terminated.