Tietra's death underlines one of the most important parts of life, that it isn't fair.

Though technically speaking if they hadn't gone to Dorter against orders they never would have gotten their achievements recognized and would have still been defending the castle when the attack happened, But the cause and effect there is so remote that it is equally possible that staying at the castle would have caused something equally bad to happen.

Bottom line, Ivalice sucks to live in.