It seems to me that the best thing any really serious professional hunters and other heavy nen users could do would be to gain a technique to purge foreign nen. Considering that I find it unbelievable such skills apparently are rare. I know if I was now in Killua and Gon's shoes, seeking out and learning that would be among the first priority, no matter how many years it took. They have certainly seen enough to know the uber value such a technique would have.

The development in the ant colony seemed logical. It's not all up to pheromone control anyway; the ants are too intelligent for that. So, it was a combination of such chemical control and a chain of command. Even with the queen still alive, we already saw the chain of command was shaky at best, but it somewhat held together until the king was born. The king, naturally, doesn't give a shit since his purpose ought to be to move elsewhere and create more queens and thus more colonies. Well, going by real insect analogy he should breed with queens from other colonies, but I doubt he could find one close enough to a human, so I assume he's just going to rape human women and wish chimera ant queens were born from such unholy copulation. Unless he's so genetically flawed he can only kill and not breed at all, which honestly wouldn't surprise me at all after his introduction.

I don't see why the hunters would want to spare a single chimera ant. They have no human ethical qualities and only view humans as food. Although listening to Colt makes sense since it's free intel.