From what I understand, a lot of the IF's "people", even those they felt very close to, left them once they were arrested. Only a handful remained really loyal, and brave, enough to remain with them until the end. I don't think that necessarily means they "betrayed" them, there could have been many reasons for that. I would imagine most of them had families of their own and had to think of their safety and well being, and there is nothing wrong with that. So just because Devervenko did not follow them, it doesn't mean he betrayed them. But I wonder why Vyrubova fixated specifically on him to accuse of betrayal, and not anyone else...