Re: Can you accidentally miss Leliana's butler decision?
Have never heard of anyone missing this conversation... Interesting. Wonder if that will mean she's hardened by default?
There are so many different decisions in the game (such as whether to do Champions of the Just or In Hushed Whispers), are you really only going to play it once? Can always soften her in a different playthrough if you've missed it this time. 😉 Really, the hardening/softening of Leliana doesn't have a huge impact on the game, there's one personal quest of hers later on where it makes a difference, and it can possibly make a difference in the end of game slides, depending on... things. (Don't know how much you know, so trying not to spoil things for you).
As I remember it, the conversation happens after you catch her praying/being mad at her god. An agent runs up to her, they talk about a traitor, and after a bit you can speak to her and influence her decision on what to do with said traitor. I've never missed it, so no idea if it re-triggers. I'm thinking it won't, though.
If you're really curious, you can PM me a link to your save file and I take a look at whether Leliana has been softened or not. Won't change anything (well, I probably could, but I won't), but at least you'll know.