He should file a hearing request (which he really should do with an attorney's help, but he doesn't have to) asking for temporary total disability benefits from the date of his injury (and, presumably date of leaving work) forward and continuing. He should treat with another doctor; he can choose one (if he/she accepts workers' comp insurance), since the panel of doctors appears invalid.
There are several questions I'd like to ask you about your scenario here to see if the light duty job offer complies with OCGA 34.9.240. However, I would not quit work in favor of unemployment, as unemployment is taxed, adn workers' comp benefits are not, and you can't get the full amounts of both at the same time. Plus, if you're still hurt, you're likely to take a long time to "seek work somewhere else." Get well first. Feel free to email me for more information at firstname.lastname@example.org; I...
It's fine for an employer to fire you after a workers' comp injury in GA (under state law, at least). You must start looking for suitable (ie, within your restrictions) work immediately, however, if you want to keep your workers' comp case alive.
Sounds like your adjuster and your current treating physician aren't looking out for you, but I'm not surprised to see that. As the others have said, you need to make a change.
Incidentally, I'm convinced that "work hardening" is a way adjusters and doctors punish people for the crime of getting hurt at work. I've never seen it help anyone; it invariably causes tremendous pain and misery for the participant.