After 51 sessions, we finished.
Despite using Path of War and some 3rd party feats we lost 15 PCs, 5 NPCs, half army and almost the sanity of the former Black Rider, my PC. She died only once, 'cause she was turned to stone; our damage dealer managed to pull things off and saved me with the help of a kind merchant of the stars. Saving throws were never my thing. But in the end we prevailed, but at what cost? My PC was the only one to survive from the original party gathered at Heldren. At least my PC has Greta now.
For some reason, book 3 was the deadliest.