もっと早く出発すれば、間に合った___。
Q. Which ending expresses regret about a missed outcome?
Translation
If we had left earlier, we would have made it.
Explanation
Sentence-final のに after a counterfactual conditional expresses regret or reproach: 間に合ったのに 'we would have made it (but didn't)'. ので/から/ため give reasons and cannot close a counterfactual like this.