Realistically what will happen is NJS will have the 20 smaller planes and do what they do now. Mainline will get the 320/21s and/or maybe a big version of the A220.
They will threaten to give the flying to NJS at the Mainline negotiations and threaten to give all the aircraft to Mainline at the NJS negotiations. The fact is they won’t do either of those things as the result of doing that will be too expensive (massive redundancies/crew shortages ect).
The most important thing for pilots is to remember who the true enemy is. Don’t listen/fall for the BS at the town halls that will be thrown at you. The threats of “it’s ours to lose” and “it’s important we reach an agreement quickly” is all part of the game. Don’t forget that folks!