In the current game state, it is insanely easy to miss out on Act 3 romance content with Astarion (or have it bug out as it happened with me), if you have a steady rotation of companions in your main party as you are completing Act 2.
After showing Astarion's scars to him, he mentions that he needs to speak with Raphael. So, the next time a player sees Raphael, they should bring Astarion to him immediately:
- This will always happen at Last Light Inn because the scene with Raphael isn't triggered
unless the player interacts with him.
- Outside Gauntlet of Shar, the scene with Raphael is triggered
as soon as you come to the entrance of the building.Looking at the map position and considering the amount of game content between Last Light Inn and the Gauntlet, you could have
anyone in your party. Astarion being a party member at that point is
completely based on chance.
You can always try and have the player lock-in the romance with the Araj Oblodra conversation, but there is nothing to clue-in the player that they even need to start a conversation with this random NPC vendor. Any player can very easily miss out and run past this NPC - the player won't have any objective/reason to stop and chat with her beyond shopping

.
Her existence isn't previously mentioned as a matter of curiosity by any party members either.