A and B are both members of a full core fireteam. Enemy C activates within A's LoF and B's ZoC, but outside B's LoF. A declares BS attack against C. B opts not to ARO so as to ensure that A will have the +3 bonus for a full link. C opts to shoot A. At the end of the order does B now get to use Warning! to turn to face C? 1) Yes, because B did not declare an ARO. 2) No, because B is considered to have declared the fireteam's ARO - bs attack - which became an idle because B couldn't shoot. B could have instead opted to not ARO at all and retain Warning!, but then he would have left the fireteam and A would not have gotten the +3 bonus.
1. Fireteam members individually declare AROs. "In the Reactive Turn, all the Fireteam members have their own ARO to any Order declared in that member's LoF or ZoC." The restriction is that if they declare the ARO it must be the same for the whole Fireteam.
Yeah, that's always been my reading. My opponent yesterday was of the view that "no ARO" is itself a declaration which will split you out of the fireteam if the fireteam's ARO isn't "no ARO." Maybe the answer is that the other three fireteam members aren't in LoF or ZoC of the active unit, so they have no choice but to declare "no ARO" yet that doesn't break them out of the fireteam. So "no ARO" can't constitute a fireteam-breaking response or fireteams would be breaking constantly.
“No ARO” is an ARO declaration is a somewhat common misconception that leads to all sorts of problems if a person thinks about it. For instance: Hidden deployment would automatically reveal: “The Hidden Deployment state is automatically canceled whenever the trooper declares any Short Skill, Entire Order or ARO.” And you’d automatically set off mines by being given the opportunity to declare an ARO. The game does not work that way.