Mentuhotep II expedition to Jebel Uweinat
Recent discoveries tell us that the ancient Egyptians travelled to Jebel Uweinat. An inscription discovered in 2008 tells us that Mentuhotep II, first Pharaoh of the Middle Kingdom, or his emissaries, reached Uweinat. It would have been made several thousand years after the end of the great Wet Phase. However, Jebel Uweinat would still have been more verdant than it is today. Archaeological evidence shows that Uweinat continued to function as a stopping point for travellers and traders on the route between Egypt and possibly Lake Bodele in Chad, south of Uweinat. Even at the time of Mentuhotep II, this lake would not yet have dried up. (See the Blue Marble 3000 time lapse map between 4000 BC and 2000 BC, in the right side bar under "MAPS".)
The description and translation of the Uweinat expedition message is described by the Fliegel Jezerniczky Expeditions team (link). Again, their website is an extraordinary source of information.
Additional research, although somewhat unproven, does suggest that from Uweinat, the Egyptians either travelled to Chad or traded to acquire foodstuff from Chad. Based on the Mentuhotep discovery, the extent of this Egyptian-Chadian relationship is now under investigation by researchers, including Thomas Schneider of the University of British Columbia. He says: this is "a route where not just physical commodities (but) also ideas, concepts could have entered Egypt. Egyptian intellectual history needs to be at one point re-written. There are influences from regions that we never believed, ten years ago, that there might have been influence." (link)
The Mentuhotep II discovery doesn't tell us directly about the destiny of the West Phase Jebel Uweinat herders, but the evidence of this continuously used trade route does indicate two exit options: Lake Bodele and Lake Chad to the southwest and the Dakla Oasis to the northeast.