I'm not sure "compassion" quite fits the loss a day's holiday, even if said holiday is of (fingers-crossed) the once-in-a-lifetime variety.

The hotel at JNB doesn't have to be "dingy", and the op will have excellent company there

Think of itas an adventure rather than a tragedy.

The airline has preserved as much of the routing and timing as possible. The op-couple get back on the day and at the time planned: if they'd got back a day late I can imagine less generous souls than the op would be claiming additional hotel nights and compo for the delay.