If the consequence of the failed diplomacy was an interesting complication instead of complete, game world-ending failure, then you don't have to fudge the roll.

If the group agrees on the lethality of the game, then you don't have to fudge the roll.

I don't fudge rolls, and I'm quite up front about it when I run for new players.

If the consequences of the failed diplomacy were an interesting complication instead of complete, game world-ending failure, then you don't have to fudge the roll.

If the group agrees on the lethality of the game, then you don't have to fudge the roll.

Establish expectations with the group when you start the game. For example, I don't fudge rolls, and I'm quite up front about it when I run for new players. I would rather engage the system on its terms and watch the game occasionally take some unexpected twists as a result of play. If the roll is going to be fudged, why roll?