No one knows the future - but all we do know points that the future is far more optimistic than people realise. If Africa fails to reach 4.3bn then it will most likely be because of faster prosperity and not due to the pessimistic causes you mention.
To illustrate the point: The last 40 years have been the worst we will see in terms of stability, economic growth etc .... yet Population growth in Africa thrived and the % of people living in poverty reduced dramatically and the current population is healthier, wealthier, and more educated than ever before (https://ourworldindata.org/grapher/above-or-below-extreme-po... ).
To illustrate the point: The last 40 years have been the worst we will see in terms of stability, economic growth etc .... yet Population growth in Africa thrived and the % of people living in poverty reduced dramatically and the current population is healthier, wealthier, and more educated than ever before (https://ourworldindata.org/grapher/above-or-below-extreme-po... ).