Thanks to an interview with Taliesin Jaffe, voice of Thancred, we know at least some of the Scions and other members of the existing vocal cast will survive, because they've been called on to do an apparently-substantial amount of voicework for the expansion (and, according to Jaffe, he was "really impressed" by the quality of the writing).

I fully expect there'll some, ah, pruning of the cast, however. Please look forward to it.