Adnul Irongut doesn't die at 0hp
The percent damage dealt per drink does not seem to be exact. For example, join a game, drink, and you’ll see you do not lose exactly 20% (though the tooltip says 10%); you’ll likely have a spare 1hp. This is likely what happened to your Adnul; he had spare HP that kept him alive. It’s irritating and should be corrected, but it is explainable.
I got him to seemingly 0% twice, then he spammed critique like crazy while belching and using fake and drink water.
>_>