I mean, I know that somebody at the very top ones a lot more than 50% of the population gone, but I feel pretty confident in assuming that they would be perfectly happy with 50% as a starting point, and if we assume that the "vaccines" they issued will protect against some form of a biological weapon that they are planning to release (I don't know what kind - I don't think viruses are real - but the "vaccines" could very well be protecting against something completely different), then they would be reducing the population by half, and a half that would be dying would be the people that are most likely to fight against them, and then from that point they could do whatever they wanted, including further cutting the population down.

If we are trying to imagine the worst case scenario, And we are taking our egos out of the equation, then we have to come to the conclusion that, if this truly was a plot by the evil people behind the scenes to get rid of half of the population or more, I can't imagine a more realistic scenario than what I've described.