grammar - Sentence ending に and のに compared to their non-sentence-ending form

Consider these:

[A] 僕はいい仕事があったら美智子さんと結婚出来ただろうに

[B] 僕はいい仕事があったら美智子さんと結婚出来たのに

Is に in [A] related to the case particle に?

Is のに in [B] related to the use of のに as a conjunction in mid-sentence?

Is it possible that their sentence ending usage originates from elision? I.e.,

[A'] 僕はいい仕事があったら美智子さんと結婚出来ただろうに(Elided content)

[B'] 僕はいい仕事があったら美智子さんと結婚出来たのに(Elided content)

Or have I no choice but to learn them as another atomic concept?

Answer

The に in だろうに historically comes from the case particle に, but in present Japanese, it should be considered a different thing. (Many things in Japanese that look like a particle actually do come from particles. Even the conjunction が as in 食べてみたが、まずかった is originally the nominative case particle が.)

In both cases, the continuing part is elided as you correctly suspected.

僕はいい仕事があったら美智子さんと結婚出来ただろうに、(いい仕事がなかったために、結婚できなかった。)
僕はいい仕事があったら美智子さんと結婚出来たのに、(いい仕事がなかったために、結婚できなかった。)

The reason it is usually elided is because its content can be reconstructed from the remaining part. Because the condition is a counterfactual condition, the continuing part, which is the reality, is simply the negation of the remaining part. The reason the condition is counterfactual is due to the use of past tense in the consequent of it. Past tense is usually used for facts that already happened, and cannot be changed in normal circumstances. Putting a past tense for a conseqnent to a condition implies that you are referring to a situation that had not happened. It is similar to how the English subjunctive past can mean a counterfactual event of a present time.