As far as I'm concerned, because the Rotapriest's Concordance starts as a roll of 1d4+1, as a key stat (so it goes from 2 to 5) and it cycles across that range endlessly, there is no legal input which would get you 0 when put to the i. If you somehow get to that result anyways, then how about: the Rotapriest hits a snag in the wheel, whose pressure is cosmically only resolved via the dissolution of the Rotapriest, who resets to 2 Concordance and gains 50 bad luck.
In terms of your confusion with how it works, that makes sense! Here is a blog post about the design ethos behind the Rotapriest, mainly about why it's written like that. Thank you for your interest!!