For all the reasons you note, people need to decide what their personal trigger point is for leaving, and how it is they will leave. Planes only have so much capacity, and even that can be reduced in a developing emergency. Where to go and what to do once there are critically important questions too, but having answers to that won’t help if there isn’t a solid plan for when and how to leave.
Are there forums or other venues where some might have the inside scoop on the condition of the grid in SA? Most governments tend to minimize the extent of problems and risks with any situation but sometimes there are insiders who know the real score. A grid failure wouldn’t allow time for folks to exit in an orderly manner and so it is imperative to determine what the odds of a collapse really are.