The transition which could replace the word thus in this sentence is definitely consequently.
Workers bravely set dangerous explosives in the mountains by hand to make passes for railroads, and consequently hundreds lost their lives.
The answer is C: The value of promises.
By saying at the end "That peace I have never broken.", the speaker emphasizes that he or she has kept his word, has done what he said he would two years ago, in other words, he or she has kept a promise. Keeping a promise can be very valuable in society nowadays, it shows the integrity and honesty of a person.
If I'm understanding you correctly (sorry, I'm new at this) It sounds like you are describing an accident that either didn't actually happen, or was minor compared to what could have happened. I would call this a "near miss" or "close call"
Explanation:
For example: I had a near miss today when a dog ran out in front of me.
Or: He had a close call when his foot almost slipped over the edge of the cliff.
The irony is that they are smiling with “torn and bleeding hearts”.
The idea it emphasizes is that they are smiling to hide their pain.
The overall message revealed by the irony is that they are in considerable emotional turmoil and faking happiness to mask their distress.