Honestly it may be a viable path they can take. Also would be interesting if that actually happens I know quite a bit of people would be super happy with the final outcome of a final defeat for her without a redemption path. However, i still think it's possible for them to use the "betrayal" to gain some sort of sympathy if it backfires on her and then Anduin or even our own characters have to save her from oblivion in lue of her helping us taking down the Jailer. Where not necessarily redeeming her but providing closure while ending her reign of terror. I still think if there's any sense in having Tyrande wielding her Night Warrior Powers, that she would have so sort of hand in felling Slyvannas or at least reconciling the rage within her and letting go of her grudge and go back into the light. Probably killing her too in the process, sort of a two birds and one stone deal.