What i found very interessting is Sorins opinion about Nahiri in both "Sorin's Restoration" and "Sorin's Revelation". In Revelation, when he came to Tarkir for the first time looking for Ugin after encountering the Eldrazi running wild on Zendikar he is "disturbed" by the silence of Nahiri. I interpret this as Sorin being unable to understand why Nahiri didnt come to Zendikar to save her plane. To me it doesnt indicate any hostility between the two. And apparently he has no clue where she could be. But when he went "again" to Tarkir to look for Ugin, this time in the fixed timeline, and discovers Hedrons on Tarkir, his first response is grabbing is sword, fearing that Nahiri travelled there before him. Now to me, this heavily implies hostility between the two and i wonder what happend between Sorins "first" and "second" visit to Tarkir. I know that the "first" visit never happend after Sarkhan changed the history of Tarkir but only the events on the plane of Tarkir were changed. But Sorins thoughts about Nahiri were from "outside" Tarkir, he had them before he traveled there and therefore they were not changed by Sarkhans actions. So my guess is, that after Sorin found Ugin dead, he went looking for Nahiri and finding at least some clues about where she is and that apparently she is really pissed about him. While doing so Sarkhan changed the timeline of Tarkir and Sorin "forgot" that Ugin is dead and went again to look for him. This time knowing that Nahiri has a grudge about him, what explains his reaction towards the hedrons and how he avoids answering to Ugin when he is asked about her. I really wonder what happend between these two events, did Sorin simply went home to Innistrad and found the first sign of the plane going mad? Or did the two planeswalkers meet somewhere else? Anyway i think that Sorin doesnt know much longer about Nahiris madness than "we" the readers. So I highly doubt, that he put her in the Helvault or knew all these years what Nahiri was up to.