Judges,as stated, are there to rule on law and not politics. However if a "treasonable" act is undertaken by Jacob Zuma then this may be construed as unlawful and would then be a case for the Judiciary to become involved.
In my understanding a treasonable act is one which is an act against the country, and the result of the firing of competent ministers which has been to the detriment of the country could be construed as such an act, especially as dishonest incompetent ministers were retained