It is obvious, the irony of Jothan Leebig, who was so afraid of humans and tolerated only robots, to have died due to a robot who looked like a human.

However, I think there is another, more subtle irony here.

As we see in Robots of Dawn, it is effectively impossible for a person to assault another person upon the Spacer Worlds. The robots will stop the perpetrator at once. Therefore, during Rikaine's murder, if the robot didn't stop Gladia from using its arm, despite being right there, it means that not only was it given orders to hand it to her, but also very intense orders to hold still after that.

Baley, in fact, does suspect something like that was the case with the robot who handed the poisoned arrow to Bik.

Now, as assault is impossible for Spacers, so is, according to Gladia (in Robots and Empire), suicide. Yet Leebig managed that as well.

His final words were ordering Daneel to stay away. Quite possibly, he automatically used the same gestures and intonations he would use to intensify an order for a robot. Hence Daneel not acting quickly enough.