Where would they use as an alternate? Windhoek is 1,367 nm on the GC from St Helena.
And to ensure you have a solid escape route = div altn for mum as well. People talk about the B734 being better than B738. There is also the B737NG. In the environment where I operated all three I can't remember having any significant landing difficulties. NG slippery in descent, yes. However, there was a significant difference in engine & wing performance between classic & NG in terms of payload & range. That might have more affect on such a route than the rock & roll of the last 500'.
RAT 5, I agree.