Yeah, whenever they have content like this that arrives in batches it's designed to not lock you out for having done earlier material that might have dropped months ago. The Behemoth will be sitting there in the village waiting for you as long as you didn't kill him in the first place, they just removed him from it in the builds in between because there wasn't anything to do with him yet. Presumably at least part of the idea was to cut down on people asking 'When will X be implemented' by keeping him out of sight and thus out of mind until it was ready. The same thing has happened before (Jael'yn for example just vanishes between 3.0 and 3.15 when her first batch of post-WC content landed) and it will undoubtedly happen again.