Multi-Part Chapter Questions

I’ve been fiddling with a project where the gimmick is that it’s one singular chapter with multiple objectives that appear as the player progresses. The player starts with two units in a closed-off area of the map (in which the way to the rest of the map opens up later) and the goal of defeating a boss. After the fight, one of their units leaves permanently , and the other unit is automatically teleported to a different part of the map to where they meet up with another group.

The problem is, I can’t find a way to do that transition into the second ‘segment’ without one of your two units messing up due to still being considered the ‘active unit’. I’ve tried triggering the event via an AFEV that triggers on the boss’ death quote, through a Seize event and an AREA event where the player simply waits on a specific tile, but each method leads to the unit that triggered the event getting put back on the spot they were on after the cutscene ends.

I know the Final Chapter of FE7 is split into two parts, and it even seems to go back to the start of the Player Phase when the map transition happens, that’s kind of the effect I want to capture, just with the added effect of one of your party members leaving. Does anyone know how to do something like that? (And sorry if that all seemed a bit wordy)