The Fireteam Cancellation rules state: The Fireteam can be cancelled voluntarily by the player, with no expenditure of Orders or Command Tokens. But when can you do so? Even after the first short skill of an order spent on the fireteam? Even in the Tactical Phase, to gain the impetuous orders of impetuous fireteam members? http://infinitythewiki.com/en/Fireteam_Cancellation
Yes. At any time, though juggling Impetuous cancellation through command token use is just about the only practically applicable case for it.
So, if you cancel the fireteam after the first short skill of an order, does every former member still have a second short skill, or noone?
Well, that's an excellent question. I think, much like dismount not bring usable on the second short skill, you'll have to accept that once an order has been spent on them, you can't cancel a fireteam until you've finished that order, for the sake of your sanity if nothing else.
Mechanically they are still activated by the order but no longer part of the Fireteam. The Leader in this case would keep activating while they will not. For purposes of ARO this doesn't matter since any Delay will still be functional to declare after the Leader's second short skill. All you're really doing is hurting your own chances here by robing yourself of the bonuses, so the big question is: Why would you? P.s. Remember that All At Once applies to everything in the order, including skill validation.
Came up in my meta. I think it was because of Exile. And if all still would have their second short skill, it would be a 5-man coordianted order with full burst. But keeping only the former leader activated sounds reasonable.
I thought you were ;) I asked this question myself two weeks ago and IJW had to remind me what the All At Once rules actually does - i.e. you can't escape Exile if you started the Order as a Fireteam, you have to cancel it before spending the order.