I'll set up the question with an example.
Units A and B are in the same sector with enemy units 1 and 2. During the combat phase, Units A and 1 are engaged and units B and 2 are engaged. There are no attempted/successful disengagements in that end phase.
In the next round, all 4 units are obviously locked in place and no movement can take place for any of them. Then in the combat phase, units A and 2 begin a new engagement and B and 1 begin a new engagement. During that end phase, the engagements of A/2 and B/1 have to be resolved to see if they end.
The question: Have the engagements between A and 1 and B and 2 "naturally expired" or are they also still in effect. Does A have to check to disengage from 1, even though 1 is (this round) focused on shooting at B?
Supporting rules:
Ending Air-to-Air engagements, Alpha Strike pg 61.
Ending Aerospace engagements, Alpha Strike Companion, pg 83.
While the rules don't mention the possibility of engagements ending by having the participants simply deciding to stop shooting at each other, my question is essentially is that an omission in the rule or a deliberate/implicit statement that they do not end in such a way?
Of particular note is the lengthy example in Alpha Strike illustrating how to apply the rule. That example in AS cannot be applied to the example I give at the start of this post (You can't know the distance between two units that did not do an engagement control check earlier in that same turn). The example is not incompatible with the inference that engagements end when units aren't shooting at each other anymore.
Personal opinion here: I do think it would make the game more playable if engagements do end once both sides have stopped making engagement control checks with one another, even if neither moved. Otherwise, you need to maintain a chart to keep track of who ever shot at who at any point in the same location prior to the current turn. (and if you have to successfully break from snowballing numbers of engagements, after a few rounds that in effect tends to mean down to nobody can move at all until the other side is wiped out completely)
