The only thing that is absolutely certain is your own existence. The dream may be false, but the dreamer cannot be. Even for the false dream to exist there is a need of a real dreamer; to be deceived, at least somebody is needed to be deceived.
The world may be illusion, but who is an illusion? At least some consciousness is needed, absolutely needed, categorically needed; without some consciousness the illusion cannot exist. The rope may not be the snake, the snake may be the illusion. But the person who has the illusion is not an illusion himself.