What about 'conspiracy before the fact.'
Conspiracy for starters requires more than one person to commit and it requires said people to actually take some preparatory actions before any court would convict, i.e. some level of definite commitment must be proven. Three drunk people around a table talking **** about robbing a bank does not constitute conspiracy to rob a bank. If they go out and start buying appropriate tools then you might have a case.
In the case of the above-legal-limit pilot the defense would argue that his professional and personal conscience might have caused him to exonerate himself (by calling in sick or too fatigued) at the last minute, causing no more than a delay in departure while the reserve was called in. If he had instead already taken his place in the cockpit and was actually going through the engine start checklist than such a defense would most likely get thrown out and you might get a conviction, even if the plane had not yet taken off, as starting the engines will most likely be seen as actually operating an aircraft, as opposed to just doing the walkaround.
Here the pilot might have to prove he did not intend to fly
Of course you cannot prove that, it's the prosecution that has to prove that you intended to fly. Waiting until you have actually and unmistakably committed yourself to flying the plane might work better next time. On the other hand, waiting until the plane has started taxing and then stopping it to check the flight crew would be extremely disruptive, I don't think we'll be seeing that actually happen unless extremely suspicious behavior is detected (slurred speech on the RT?)