Nikolai could only watch as Ezekiel's unconscious body was taken away. Thankfully, Ezekiel himself already knew that this was the price he had to pay. He already knew this was coming. Tarah had already warned them both, but they still took the risk… all for the chance to end Mineah's curse on top of Vulcan's soul being extracted from his body. They needed Devon's demonic and overflowing dark power to extract the soul out of his body. And after that, only then could Mineah use her divine dagger to end Vulcan for good.
Or at least, that was what Tarah saw in her vision. From what Nikolai knew, things still weren't set in stone, and the Seer had also clearly informed them that she was unable to see how things would end. It could end successfully, but it also had the possibility of ending badly. Well, nothing would happen if they did nothing and just waited for the curse to take effect. In the end, doing this was still the best option.