I can really sympathise with this situation as it happened to me as well a few years ago. We hiked up the mountain and planned to come down with the cable car. But many hours later by the time we reached the Table Mountain Aerial Cableway at about 4pm, it was closed (due to high winds I think). The only way down, was down Platteklip George, and that is a very steep descent. If you are over 50 or so, it hammers your knees and ankles. We only got down by 8pm, long after it was dark.
An exoskeleton could certainly make things easier. But regardless, the WSAR (Wilderness Search and Rescue) are a group of volunteers who do a tremendous job. Contact WSAR in case of emergencies on 021 937 0300.