If I do understand it correctly, True Resurrection only works if the person has been dead for less than 200 years. I assume they picked Astarion's age especially so that True Resurrection cannot work anymore.
I am quite happy with him not having cured his vampirism by the time of the epilogue party. I think it's quite nice for "looking for a cure" to remain a possible plot hook and not a resolved matter. What bothers me is that Astarion has all these beautiful line about equal partnership, but the game does a bad job in showing this equal partnership because the PC is not equally able to express vulnerability or support.
In the couple scene after the fall of the brain, it's quite nice and considerate of him to ask what the PC wants to do next but it would help if the PC could be just as considerate in the phrasing of their suggestions or maybe even a little enthusiastic, so that the dialogue actually felt like that there is nothing these two can't handle together.
