Hypotheticals like that are uninteresting because there are only two ways it can go. The first is that you can find a way out of it, and then you say, do we need the magic spell for anything? Is knowing about it useful to preventing it from being used? Then people need to know.

The second is that you're stipulating the information being available is going to destroy the world with high probability and no possible means of mitigating it. Then anything else gets drowned out by the end of the world, but only because you're stipulating the outcome.

Which you can't do in real life, not just because the real probability of the hypothetical is so low but because there isn't anyone who can be trusted not to fudge the numbers when they want to censor something. Should it be censored if there is an absolute certainty it will destroy the world? There isn't much room to move in that one. Should it be censored because somebody claims it's really bad? Nope, because it's way more likely that they're full of crap than that it's actually going to destroy the world.