LH has rebooked passengers booked to Germany (which has a travel ban for SA flights in place) on corporate sister airline Austrian to/via VIE (no travel ban in Austria) and flew back an empty plane on 12/22 when the travel ban went into effect. When this became known there was quite a bit of bad press...(
link)
Others I know have rerouted via Namibia (start in WDH) .
With VS and partners not flying anwhyere nearby (the only other destination in Africa is Lagos - and getting there is expensive and cumbersome even not taking covid restrictions into account as there's no direct flights) it looks like you're out of luck here if VS won't rebook you onto another carrier.