That's for the most part up to the National Mediation Board (NMB). They are the government entity that gives the authority that allows any group bargaining under the Railway Labor Act (RLA) to seek self help.
If the NMB feels that it has exhausted all possibilities between the two parties to reach an agreement and that the differences between those two parties are irreconcilable, then it has the discrestion to release both parties to self help only as a last resort. In essence if the NMB releases the parties to self help then it has failed to do its job. The NMB's mandate is to first and foremost prevent a work stoppage and to help facilitate an agreement between the two parties.
The NMB is presided over by a three member board, all of whom are appointed by the President of the United States. By law one of the three members of the board has to be from the minority party(Dems currently).
Currently two of the three members are Republicans who work for an administration that has publicly stated that "no airline will go on strike" under its watch.
Also currently the head of the National Mediation Board, a woman whose name eludes me, has been reduced to nothing more than a political puppet with no real power to set a course or direction for the NMB. In a sense the NMB is currently in a state of chaos.
The NMB is supposed to be neutral to the party's postions and therefore be able to better facilitate an agreement. But honestly if the NMB believes that your group's proposals are unrealistic, unattainable, or just plain out of reach then they certainly aren't going to be in a hurry to work through all the steps of the RLA and eventually end up with a release.
So you ask how long it's going to be before XJet pilots can expect a release from the NMB. No way to know that. Under the current administration it won't be any time in the near future, translated at least within the next 6 months. But with the election looming and a supposedly "labor friendly" candidate that could win that all could change.
So long answer to a simple question is: probably no time soon.
As far as probationary pilots and a strike.... First off you are correct in that no pilot, probation or not would get paid during a strike. Having money put aside to have at your discretion during such an event is one way to make it through. That's not necessarily an option for everyone, especially folks just starting out. As far as what a probationary pilot is required to do during a strike....You have to do exactly what the company tells you to do. You unfortunately have the support of the Union but not the protection of the Union. Besides what would the company have you do, come in and sit around in your uniform? Can't operate the airplanes without Captains. So normally you would probably have to just help out "behind the scenes" as much as possible to protect yourself.
Hope that helps.
This issue of a strike and the NMB is far more complicated than most of our pilots realize. This is why they need to educate themselves on this as well as all the other issues that went into the crafting of the current TA.