Fudging, whether it's die rolls or it's monster stats, is never a good idea.

You are playing the game to find out what happens. In this case, you've a situation where a die roll can end the world. Just go with the roll. Make sure everyone at the table knows what happens if the roll goes one way, and what happens if the roll goes the other way, and then let everyone see the roll as it's being made (it's a PC making the roll, right?). Be clear about the DC and mods and stuff too. Let everyone see the stakes and then roll.

Sometimes, if a die roll ends or drastically alters the world, that can be pretty cool. If the world ends you can always make a new world.

The Kang Civil War in the backstory of the Talislanta game started with a PC rolling an unexpected 20 in a session, events that became canon in future editions of the game.

The difference between fudging 1% of rolls vs 100% of rolls is (albeit definitely non-zero) smaller than the difference between fudging 1% of rolls vs **zero**. Try it. Sometimes frustrating or boring or disappointing things happen. But sometimes truly epic and awesome things happen.

I love zero-fudge play. That also means refraining from scaling monster HP, abilities etc on the fly.