Im imaging this situation atm. I havent found something about with the search function

2 Players AB (in the same aly) have squads in OP or colo

Now player A leaves the aly. Will the squads fight against each other, right in that moment or at the enxt tick change?

If not
Will they fight against each other if player B leaves the OP and after tick change he retunrns the units (will that be possible?) ?

If player A left the alliance, and player B's units were still there (presumably in Player C's outpost or colony, a 3rd party) they will not fight at the moment or the tick change.

If player B left and came back, player A's units would still be floating there. They can't defend property that isn't theirs. Now if player A did that, left and came back, I believe there would be a battle.

I recently had a situation where 2 of my alliance members had a few squads each on an OP that used to belong to a member of mine, but that member changed alliances.

So now those squads of mine were floating on that OP, despite it belonging to another alliance.

Then an enemy to the new alliance of my old member (confusing, I know...) attacked that OP.

None of my current member's squads were hurt, or even involved in the battle, and I believe they are still floating there at this moment actually...

My guess is that they are using that OP as sort of a camp, can't attack from it, and even if the other person razed it, it would stay as a camp.