Common ProblemsI left the Exodar before picking up "Into the Night," and now when I try to walk back in it's blocked.
In order to travel to Argus, you must complete the quest chain which includes Into the Night.
If you abandoned this quest or did not pick it up, return to your faction's capital city. While there, Alliance players look for Vereesa Windrunner at Stormwind Harbor and Horde players look for Lady Liadrin at Bladefist Bay outside Orgrimmar.
Speak to the character and choose the option to return to the Exodar scenario. Once in, head left into the Exodar and use the Lightforged Beacon to travel to Velen, who offers the quest.