Well, the henbane finally lost what was its fifth or sixth go-round with the aphids. I walked in the other morning, and it was completely wilted, with lots of brown. I tried watering it in case it was also dry, and drenched the leaves in a water-diatomaceous earth solution, but no, dead.
After some thinking, I believe I will give it a funeral, as it was a sacred plant. Dry it out some and then burn it with ceremony (outdoors, henbane smoke is potent).