If Anauroch were bordered by mountains to the west, south and east (including the Desertsmouth peaks presently in existence), how might that affect the region? Trade routes would be hindered/obstructed, certainly; the Zhentarim might not be so eager to use its wastes as a means of bypassing more civilized regions (unless they knew of a secret path...). Fewer monsters would trickle into The Stonelands. What else?
Stand with anybody that stands right. Stand with him while he is right and part with him when he goes wrong.
Too many factors. Would people just use the Underdark or a tunnel through the mountains? Would these points become major cities because of their importance? Would people seek to control both sides (but if its Underdark passages, will there be multiple entrances/exits)? Would someone setup a skyship ferry service that just goes over the mountains? If that were the case is there a caravan service that stays IN the desert such that people travel to the skyship, sell their caravan wagons to people leaving the desert, and then buy a new set of wagons on the other side?
For skyship ferry services, I would expect Halruaans to charge steep fees for transport. They would not be eager to sell their trade secrets of skyship design. For Underdark routes and tunneling through mountains, that is inherently risky with the additional risk of freeing the phaerimm under Anauroch. The Zhentarim would likely not bother maintaining the Black Road with the expense and risk. I would expect trade routes to go around the mountains.