Jo'burg is an inland city. South African larger ports are Cape Town and Durban. Other cruise lines often include planned stops in the Seychelles, Mauritius, Madagascar and Reunion Islands on the East side of Africa. On the West, Walvis Bay, Accra, Dakar, the Cape Verde Islands and the Canary Islands are often called. So many port options, but, to fit into the time frame to get to Athens would surely be a challenge.
Let's hope it doesn't come to that, and not just for UWC, but, so that all the unrest, shelling, mayhem, loss of life and heartbreak in the region can end peacefully, as soon as possible, and for all involved.