Bard influences Runeterran history in very different manner than the Darkins. Where Darkin directly influence key events in history through conflict and bloodshed, the Celestial passively pushes the world back to balance during its most desperate hours.
Bard is not concerned by the mundane actions of mortals, he only acts when larger dangers of cosmic significance threaten Runeterra.
For example, if Bard intervenes it's to influence something in another dimension 10000 years ago. Bard is not there actually to save you, he is saving you because one of your descendants might have an important part in the future, meaning that your life must be secured (at least to a certain point) for that to happen.
I feel like if he failed, which I doubt he ever has, the dimension in the future won't have you because he failed to save you in THIS timeline.