Reminds me a bit of a previous campaign (not DnD). We (the party) spent so much time and attention murdering and threatening our way into a coup against the sickly King that we stopped paying attention to anyone else in the story.
Then in our campaign finale, we flub every single roll to execute the coup, and our whole plan gets hijacked by a more competent NPC to seize power for herself. Queue TPK* while we all get hunted down as traitors.
* Except for the party poisoner. He was happy to spend his life in prison so long as the new government let him brew poisons for use against enemies of the state.