That one I can answer. 'When one or more members leave the Fireteam, the player must recalculate the number of members to check if a Fireteam Cancellation occurs, or to determine the bonus available to the members during that Order if enough remain to compose a Fireteam.' My emphasis. So the Fireteam bonus will get recalculated for the whole Order, and can potentially mean B2 against an active trooper dropping to B1.
Yea, but we now hit a chicken-egg problem that in order to declare a skill which kicks him out ot fireteam he has to be a part of it first.
But we are talking about situation when he already "used a fireteam propertry" of delaying his ARO due to SS1.
Which he wasn't entitled to do (in hindsight), because he doesn't benefit from SSL1. When you declare an invalid delay + subsequent ARO it becomes an idle even if you never actually received an ARO (source @HellLois). So there's no chicken and egg problem: it's a mammal.
A platypus aptly describes the Infinity Rules at times. But from my POV we've got a clear answer: Fireteam bonuses are removed for the whole order, being able to delay with SSL1 is a bonus therefore if you lose SSL1 your delays will retroactively become invalid. Consequently, don't delay and then declare AROs that will strip you of your bonus if you don't want to Idle.
I'm going to communicate to my group that the way to play this is as described by @inane.imp then, that answer is good enough for now. This is a good candidate for an FAQ just to be sure.
No, it could do with inclusion in the FAQ.. But that's the implications of @ijw reminding us that the rules strip the benefits retroactively: you can take it or leave it. The 'invalidly declared AROs become an Idle even if the Trooper wasn't entitled to an ARO' is in the [Solved] thread: https://forum.corvusbelli.com/index.php?posts/107876/