The buff from the elixir is not permanent. I have had it disappear after resurrecting characters that had the buff. As long as your character has at least one point of vitality it is there but die and resurrect and it is gone.
I'm pretty sure it's supposed to be permanent (it says "permanent" in the description), but I, too, have seen it disappear from a character. I wasn't really paying attention to when, but there was probably a death involved.
