You don't even have to travel through the Desolation to get to the Crystal Oasis from Vabbi. Once you teleport onto any of the new maps by any way (including guild hall exit and spearmaster's plea), you will automatically unlock the first waypoint on that same map, so you're just a few steps away from the next map. Basically you use whatever method to get to Vabbi, teleport to the (auto-unlocked) waypoint in the northwest of the map, step through the portal to the Desolation, teleport to the northern-most Desolation waypoint, step through the portal, teleport to the northern waypoint, step through the portal and teleport to the then-unlocked waypoint in Amnoon. Takes a couple of waypoint fees to get there, but nothing that should seriously inconvenience anybody. If the few silver and couple of minutes this takes it too much, there's still the story option to get to Amnoon "for free".