Red mage could take up a healer spot, though instead of just having heals they ought to be limited to the equivalent of cure 1 and medica 1. The rest could be made up by buffs and debuffs to make more healing unnecessary. Careful application of those buffs and debuffs would make minor healing adequate for 4 mans and allow one full healer to be enough for 8 mans. Of course this would be a pain to balance, so never going to happen.