When you see the ‘war preparation phase’ matching is already done, because you see your opponent, no
Matching happens somewhat before that and it takes 3 hours. So, let’s for the sake of simplicity assume that when you currently see ‘war starts soon phase’, matching is already done, it’s just not shown to you. They plan to show that in public and maybe shorten war prep phase itself… let’s see.
What player put in that ‘participate in wars’ box, that option will be valid and used for the next match up.
So, with that time constraints about phases in mind, your points 1 and 2 are true - only those who have checkmark ‘yes’ will be used in the matchmaking system and will show on the battlefield and fight the war.
Point 3, I didn’t test, but from what I understood you may be right, they are used in matching, but will be removed from the battlefield (or if they remove their def heroes). So yes, too late for matching definitely.
I’m not sure if they will end in the field or not though. In the case they are removed in the moment they put ‘no’, then if they immediately put ‘yes’, they could also end in the spectator mode, the same as any new member to alliance who comes during the war prep phase.
Again, didn’t test, just saying what looks that follows current logic.
However, I’m more inclined that situation is that their teams are in the field, and opt out will be considered from the next war on.
We always had def carried over from the previous war. However, earlier we could change def ONLY during the war prep phase (so, that 24h for which was never known when they exactly start, because ‘next war starts soon’ was without the timer, which now will come). Now we can change def any time between two wars, so we have days, not hours to do it.
So, 4, during the current war def was always fixed. They also said if player exit the alliance, team will stay, however, that doesn’t happen and that is many times already reported as a bug. That I’ve seen and yes, team is removed (but that should be a bug, considering the release notes)
So, now the question that’s left is what happens if someone switch checkbox from yes to no and other between the matchup is exactly done (because we don’t know when that happens) and war prep phase starts.
In any case, player who didn’t put full team will be removed from the field. That’s not connected with the opt out feature, however, it does support my idea - if the opt out is clicked after matching is done, your team will go to the battle.
However, if someone did that, and was counted in the matching, depending on the team strength, it usually helps to leave it even if they don’t participate - so the opponent will have more targets to take down, no matter how small, it will still waste at least one flag.
So at the end, I believe it’s ‘what was active during the matching phase’, so any change during the preparation will be for the next war. However, I have no proof for that, maybe someone else does.