What health issue made him give up on wicketkeeping? Other than him claiming to be tired I see no serious health issues highlighted in the link you shared, perhaps I miss it?
I can agree with you on him stepping down rather than being burden (which I think he was).
A player of his credentials would lose out if he took up a county contract, would he? It just seems hypocritical that he seems comitted to leagues like the IPL instead of staying on with the test team a couple years longer, SA clearly lacking test batsmen, even though he seems a burden on the team he proved otherwise against the Aussies/Indians in the last few tests. Should have played test cricket a bit more, seems to me he is more tired of playing for his country more than anything.
At this point of time, it makes sense for ABD to play T20 leagues than to be playing the "I pick what games I play for SA" thing. With T20 leagues, it does not matter if he plays a league or not, or if he misses some games in a league or not. But if ABD does that with SA, it creates uncertainty and instability and if he's not up for it, he needs to leave which is what he has done.
And please - I have barked this tree a million times in this forum. This whole fantasy of "playing for your country" is very smartly engrained into the audience minds by ICC and its member boards, for commercial purposes. You are certainly NOT representing your country if you play for CSA (Cricket South Africa) or BCCI (Board of Control for Cricket in India), etc. Most of these boards are not even affiliated with their respective governments (I know for a fact that BCCI is not). And a player selecting what he/she wants to do in their career is totally their personal choice. Any country will have adequate resources to keep the show going. How much time you spend in finding and grooming that resource is up to the skill of your respective cricket board. Why do you think players leave aside cricket games to be with their wives when they are expecting a child birth? Because personal lives come ahead (this is why I did not concur with MS Dhoni, who just further romanticized the commercial concept of "playing for India is more important than being by your wife's side when she is giving birth to your child").