However, if no reply is given within months or years, and the asset is completely abandoned, I do not believe it would be unethical to use it. In fact, I believe the opposite is true: It would be unethical to not put the asset to use. The creators' legacy lives on through their work, and I would be intensely proud to preserve that in a mission or mod.
I agree that it would be unethical not to use it, but I disagree with the rationale in a hypothetical case if the mod team and the modeler disappeared.
It would be unethical not to release it because it would force someone to "reinvent the wheel" for this particular asset. That cannot be good for the community because it diverts time and effort for something that should not have needed it. You may argue that had the asset not be leaked, nobody would know about creating a mimic of the asset in the first place. However in the hypothetical situation separate from Droid's, the model
is leaked, so not releasing it would be on your conscience.
My disagreement is when you said that the creator would be intensely proud to have an asset used in a mod. There is no guarantee that the creator of the asset would be proud if the asset was exclusive to begin with. Some assets go down with the ship. HLP has been doing great work in recent years when it comes to dumping assets after a mod has been declared dead; but we cannot ignore the cases when such an event does not occur because of the exclusivity of a particular asset, no matter how unlikely the case may be.
In Droid's "hypothetical" situation, if the team is active and the modeler doesn't want it to be released (supposing that you already asked the modeler or team for permission), then you are not in a position to release it. Your only choices of the choices given are 2 and 3, and the decision for either is dependent on how well you and the aforementioned team can gauge the release date of the team's mod, and how long you can put your mod on hold. Choice 2 puts you back to recreating the asset, but unlike the previous hypothetical situation, you are not in the ethical position to release the model. 3... does nothing for the community and only hinders your progress. It must be disappointing to be facing this dilemma.
If the team with exclusivity of the leaked asset is active, they believe that they are (in relative terms compared to recreating the asset) nearing completion, and you believe that they are almost ready to release their mod; then you should try negotiating like karajorma said. It doesn't hurt to ask as long as the benefits of time, pride, and effort outweighs the cost.
I don't know much about the situation aside from what's posted in this thread.
I mustn't have been on IRC when it was mentioned.