To improve our understanding of the liquid-gas phase separation occurring in ordinary molten salts a variety of model ionic fluids is investigated extending from the restricted primitive model (RPM) (composed of hard ions with equal size) to model reactive fluids in which a chemical reaction between ionic and covalent species takes place. In searching to improve the existing linearized theories for the RPM, it is shown that the mean-field approach of Debye-Hückel (DH) theory is very sensitive to successive improvements (ion pairing, hard sphere contribution, dielectric constant), whereas the mean-spherical approximation (MSA) exhibits, under similar conditions, less sensitive behaviour. In particular, it is shown that the good agreement obtained by M. E. Fisher and Y. Levin (1993,Phys. Rev. Lett.,71, 3826) with computer simulation data in implementing the ion-dipole interaction into DH theory with ion pairing worsens significantly if the dielectric medium composed of ion pairs is properly taken into account in a self-consistent way. However, our improved MSA incorporating at the same time ion pairing, ionic solvation and dipole-dipole contributions shows only qualitative agreement with the available simulation data.