They said their source in the article. People familiar with the matter. WSJ vets them so they know they actually are familiar. Obviously they won't be named.

If WSJ said it, unfortunately I'd say it's game over.

I doubt even the Spirit management knows yet what the exact timeline will be. They will look at where their planes are and where they need to be flown, what their air traffic liability is to maximize intake from CC processors for completed flights, they will coordinate timed comms with the unions so they all announce it around the same time, it's a 4D puzzle to come up with a plan and more often than not, the plan is announced with hours or sometimes a few days notice.