While Baum was not famous for consistency within the Oz stories, the differences between the two appearances of the Powder of Life were significant enough to affect how they were represented in the rules of AiO. But were they really intended to be the same?
David Maxine does accurately point out that while Dr. Nikidik's Celebrated Wishing Pills are indeed a product of Dr. Nikidik, the Powder of Life isn't necessarily. Though the connection is strong enough for Gregory Maguire to have Nikidik's appearance in Wicked include a demonstration of a prototype Powder of Life.
In The Road to Oz, we learn some more details of the fate of the Crooked Sorcerer. He apparently fell off of a precipice and died (this is apparently before Baum instituted the "no death" rule), leaving his possessions, including a small batch of the Powder of Life, to a distant relation named Dyna. This Powder was used to accidentally animate a blue bearskin rug, creating a rather pathetic creature.
But in The Patchwork Girl of Oz, we meet Dr. Pipt, who claims to be the inventor of the Powder of Life. He also claims that he gave Mombi (and ultimately Tip) the batch that was used to animate Jack Pumpkinhead, the Sawhorse and the Gump. He doesn't mention the Wishing Pills, so it's certainly possible that Dr. Pipt and Dr. Nikidik are two different people.
However, this does not tell us who died and left the Powder of Life to Dyna. Did Dr. Nikidik fake his own death? Or did he actually try to kill himself only to be thwarted by the magic of Oz? Maybe the bearskin rug knows. But without the lungs he used to have, he is rather unable to speak.
Although when you think about it, many things without lungs are able to speak in Oz. Maybe it's actually a curse of silence. So lifting the curse may be the first step in unraveling the mystery. Where it leads is up to you.