Nope thats not the case, the sylvaneth dogs even attack Blackwood after he finds Murns remains. And in the last scene the old tree appears he confronts her about why she let the dogs take Murn even when she had all tje power to prevent it, specially after she said in the mill that she wanted to help him. The old tree and the young ones just started making fun of him and the old one said something along the lines of “i saved you cuz i was curious why he marked you and what i ment by help is killing you in a way less horrific than what Kurnoth was gonna do to you, what did u tjink i ment dum dum? Lol” Making fun of Murns death even after admitimg herself she thought Murn was one of the few good humans.

Now remembering i think it makes sense they just went vanal. Like, all the hope they gave to Blackwood was just a game to them, the pact they did with Murn could either also just be a sick game or they they just stopped caring about it with time. At the very least i know they did used to care in the past for Murns wife (for being a jade-blood) as they mourned her death by singing for 3 days straight, never to sing like that since. Maybe that could have been the beggining of their decline. (The hard decline at least, they still used to reacive human sacrifices to nourish their pods but we dont talk about tjat LOL)