Astarion, of course, will take his own Ascension. He wants to be alive again, to live life to the fullest, to get rid of his painful hunger, to enjoy the sun he loves so much, to see his reflection again, and to taste real life in all its fullness. Astarion himself would hardly think that condemning himself to an eternal existence as a spawn is to become “the best version of himself.” As someone who has been forced to survive and exist in extremely brutal, hellish conditions, he will think rationally. A character too “good” and “moral” to sacrifice himself and give up such a chance as Ascension would simply not be able to survive and would have died while still a slave of Cazador, or would not be able to keep his mind and survive all that Astarion experienced, or would have changed radically, completely changing his attitude to ‘morality’ and to the gods of this world who dictate what is “good and evil” ("I tried them all. None of them answered." Astarion doesn't like the gods, and with very good reason).
Personally, I like the Origins variant of the game, where you make decisions based on a character's approval table, and making the decisions that character himself approves of when he's a follower. It turns out to be a sort of movie game when you don't make the choices yourself, but it's interesting to see what happens when you do, and how the story plays out.
About the romance, that's an interesting question. I liked the romance with Minthara in Astarion Origins. In the main game, Astarion approves, if you take her side, perhaps an understanding could develop between them. I felt encouragement from her during the game, and the romance turned out great. But perhaps it was purely my desire to see her romance, and Astarion himself would prefer solitude.
