I experienced the same thing (not with Smythin, but similarly accidentally while sorting out the goblins), and it was frustrating at first, but when I spoke to the Oathbraker at camp, there were dialog options for it being unintentional, and a path to reclaim the oath, and I'm okay with that, it felt very natural.
Ah, was there? I remembered an option to say I didn’t know the consequences of my action, but not one for me just not being fast or good enough to do what I’d have wanted to do. Mind you, as failing to save Smythin didn’t break my oath and I didn’t come across any other scenarios where this would have applied, it wasn’t something I was specifically looking for so possibly it just didn’t register.
