Yshtola is slowly dieing anyway so eh killing her off faster just cause she doesnt get the development you want brah people love her cause of how she is[tho i admit constant death flags on her is rather old]... in a recent interview Yoshida said whoever dies isnt decided by popularity anyway and they have already decided the fates of each main character. But yes using 'face of the game' excuse is kinda annoying to hear all the time.

Thancred had a decent character development but hes not going anywhere past Rynes growth also once hes back on the Source he will be vulnerable af unless someone can recharge his aetheric attacks like Ryne does on the First and we know Ryne isnt going to the Source atm, Urianger is interesting, after ShB im liking him more as he was forced out of his comfort zone and id love to see more of that, many ppl too from what ive seen.
Neither of the Twins will die any time soon tbh.