Life is violent. There's no getting around it. Sure, your presence may have distracted the kitty momentarily, allowing the mouse time to escape, but it doesn't matter. It's just a matter of time. We're all worm food in the end.
So can you tell I recently re-watched "The Seventh Seal"? The squire has my favorite line in the movie (paraphrasing): "It's hopeless! Don't you see? I'm trying to comfort you!" Easily one of the best comedies of all time.