Vardo's count in that time is two: Denalie and Illeanna, oh and Regno. So your previous statement, as DMs, and Vardo players have said previously, does not stand.
At the risk of revealing information I learned as a DM, I cannot elaborate- but I can say that it was NOT the Vardo that killed Denalie. She was killed, but it was by another faction inteirly, and no Vardo PC arranged for it to happen.
The Vardo aren't untouchable, and they NEVER WERE. You just don't know everything thats going on. Why don't you know everything thats going on? Your PC's. "But not knowing whats going on upsets us!" Yes. Thats the point of the gothic theme. Your not supposed to understand everything that happens.
Want me to throw out some examples? Several Vardo pc's lost their souls and were extorted to do jobs for a certian group. At one point, Julia was geased by Strahd to never be able to betray him and forced to do his bidding. The difference is when something bad happens to the Vardo they close up and keep it within the family, as opposed to telling everyone about it.
Fact of the matter is, the Vardo do what they do because they do it in a smart enough way to get away with it. When certain tactics stopped working, there was a backlash and they had to change strategies. Everyone HATED the Vardo for a good few weeks- ironically, not because of any true IC activities, because Denalie was never actually activly threatened by the family except perhaps by someone like Illeanna going off the handle. It was all derived from pure OOC bias from players who had tendencies (I wouldn't be so dramatic as to say someone had a thought out vendetta) that caused them to be antagonistic to the RVT faction group.
And that practice also countinues to this day- I know players with whom EVERY character they play makes it their mission to frustrate the faction and attack it. If this was IC I would have no problem with it, but people are just frustrated OOCly. I am becoming very frustrated with having to be constantly suspicious of everyone metagaming or meta-factioning (I invented a new term!)
The Vallaki Guard are the ones who permakill most players. For the most part the Vardo are simply a mechanism for another factions dynamics- they are used by all the other factions to do what they themselves cannot, so they tend to be the 'hand' of events. They are a MECHANISM for death, not the cause in the majority of situations.