I doubt that S.A. has any significant border control. The problem seems to be the mistaken hope that the assets of white S.A. can be saved. My great uncle’s family had the same hope for their business in Poland before WWII. A thousand days they could have walked right out and found asylum but could not take their machines or tools with them.
Unlike your Polish Great Uncle's family, it has become damned near IMPOSSIBLE to get out of RSA, which has been true for several decades now. OTOH, many Afrikaners DID leave, by hook or crook, 30 and even 20+ years ago.
Prior to Mandela, the army was placed on ALL of RSA's borders to keep the ILLEGAL ALIEN BLACKS, from nearby nations, from coming in.
Mandela relaxed it somewhat, then that practice was stopped completely, so there has been an influx of blacks, from other nations, who NEVER lived under Apartheid, to get in and stay.
When it was still allowed, the Brits and a few other Commonwealth nations allowed white RSAers, who could PROVE that they were descended from Brits, to emigrate, but NOBODY else. That all stopped a while back.
When NO nation will take you in...HOW is escape to even be a thought?