Tuthrick: It's hard to place Blood Omen 2 in the timeline, but from what I understood the events of BO2 happened, because Kain saved Raziel at the end of Soul Reaver 2. He even says something along "The Hylden, we walked straight into their trap." after he gains new memories. It was possible to change things, because of the paradox (Raziel and his spirit attached to his arm being present).

I think that Kain tried to prevent the events of BO2, especially his initial defeat, but not only that in my opinion. It's not explained and he's quite cryptic about it. Maybe because he tried to change things again looking for the correct outcome, where he and Raziel could live and fullfill thier roles instead, but it seems that he was unaware of what was Raziel's actual purpose. Kain was hoping for the edge of the coin, but didn't know what would happen exactly when it would occurr. That's how I see it.

Maybe the Hylden would use someone else if Janos remained dead, but then maybe this would cause the story of BO2 to be a lot different, especially if they would choose "the walking paradox" Raziel. However, we know that Janos was thier target and that's why they somehow influenced Raziel when he met with Kain in the Avernus Cathedral.

Tuthrick: It's also interesintg why they didn't choose Kain instead, we don't know the answer. They seem to be capable of corrupting both humans (Mortanius) and the vampries (Janos).

Tuthrick: Well, it's what I assumed when Kain said that "great harm will come of it" (the Heart that is), because at the end of Soul Reaver 2 he said after saving Raziel that Janos must stay dead. At that moment Kain acquired new memories (the plot of Blood Omen 2) and knew that Janos will be the target for the Hylden. Unfortunately that message didn't reach Raziel, because he already slipped into the spirit realm. As for why he didn't repeat that when they met in the Avernus Cathedral, I have no clue.

Why did the Unspoken/Hylden choose Janos as their target? Well, he is the last "original" vampire, so it's their revenge and they need someone immortal to "power" thier device.

Yes, Vorador was decapitated in BO1 and it's assumed that the same thing occurred in Defiance. He was the last vampire beside Kain and very old one, so Moebius prepared a public execution for him, which young Kain witnessed after he came back from the past (where/when he killed William the Just): https://www.youtube.com/watch?v=-wpPdQt6DeU

Kain's relationship with Vorador is a bit unclear. He did say that Vorador was a decadent old fool, but Vorador helped Kain when he called for him in the Dark Eden (he dispatched Malek). Plus, Kain kept his ring (as his earring) and in one of the possible endings of Blood Omen (the canon ending) he admits that Vorador was right "We are gods".

Now coming back to Defiance, the old Kain has the memories of Blood Omen 2, so he knows that his younger self will need Vorador and this might be one of the reasons why he would resurrect him. Unfortunately, we might never know whether that was the course of the story after Defiance, it's purely speculations.

As for Vorador escaping Moebius in Defiance, there are no signs other than that we don't actually see him being executed, like in BO1. I assumed it did happen, but there can be other possibilities I suppose.

VandheerLorde: Raziel has already be affected by the Hylden spirits during the Avenus Cathedral confrontation, causing him unable to fully control his emotion and listen to Kain calmly, he mentioned it in his monologue: "the madness of this place had somehow fueled my rage".

Btw about the reason that Kain survived after losing his heart, perhaps it's his fate that he can only be destroyed by Reaver as he's also a wielder of Reaver?