Why people call demise of WGA? what happen if the end date is because they won big?
For the end date of the Writer's Strike due to the Writer's Guild truly winning big would require the Film and Television Industries to completely cave-in to the demands either due to them chickening out or facing serious pressure from the other Labor Unions (If they do take sides).
The Writer's Guild in the event that they do call any Strike would need the strike to be settled in less than 1 year and any such strike that lasts more than 18 Months would likely see the Writers Guild face a completely irreparable decline since the Film and Television Industries would eventually see all level of tolerance for the Writer's Guild to be completely used up by that point. By then they start turning to the Non-Union Writers and decide to take Legal Action against the Writer's Guild through a major lawsuit.
In the event that the Film and Television Industries and the Writer's Guild ended up in court arguing their sides before a Judge the likely outcomes would be.
Outcome #1 - The courts order the Striking Writers back to work (Forcefully ending the strike), Impose a "Cooling off" period and the negotiations restart afterwards and possibly the Film and Television Industries secure an injunction preventing the Strike from being restarted.
This outcome could easily open the door to changes that would easily weaken all of the Unions
Outcome #2 - The courts order the Film and Television Industries to agree to the demands of the Writer's Guild and the Strike ends.
This outcome would be the least likely outcome.
Outcome #3 - Before the courts make a decision both the Film and Television Industries and the Writer's Guild step up their negotiations and manage to make an agreement which ends the strike and would result in the lawsuit being declared as being Settled out of Court.
This would be the most likely outcome.