So kinda confused regarding missile launchers and have a few questions 1. Can the blast mode be used on an ARO? 2. What happens if it misses because it does not have deviation? 3. Can it miss or does it have to be dodged?
1. Yes. You can declare the BS-Attack Aro with the Weapon Mode and Ammo 2. If it misses the Attack/ARO dissipates and nothing happens ... Think missfire 3. see 2.
keep in mind that even if your roll is beaten, but you've rolled below your target number. Your attack "misses", but the template still goes down for any other models that may have been affected by it.
I'd put it differently. If you miss entirely (dice is greater than success range), then template could as well be removed - it's not hitting anyone anyway. Otherwise, as per Impact Template rules, it's a separate face-to-face with everyone involved, although shooter's modifiers are derived from his original target. The latter is actually why completely missed impact template could as well be removed - since you won't get different success ranges for different targets, such template is a miss for everyone who could've otherwise ended up under that template.
Fluff wise all explosive munitions deactivate if they miss to avoid collateral damage hence no deviation.
Missile Launchers (and Rocket) are perfect AROs against active Fireteams. The Fireteam can only declare a shoot attack with the Link Leader, so if you shoot a secondary member, the team must all declare dodge in order for any of the models to have a chance of avoiding it. If they declare shoot with the leader you will each roll your attack unopposed and, assuming you hit, the link will eat a missile. This may not always be a valid option for you as your opponent will usually "slice the pie" with the Link Leader, but is a deadly tactic employed by TO missile troops like Swiss Guard and Noctifers who can appear unexpectedly :)
If only fluff could justify deactivation of ammunition if it was hitting friendly guy who is engaged with enemy....
That's just an extrapolation of modern IFF systems. https://en.m.wikipedia.org/wiki/Identification_friend_or_foe Template weapons do not activate if they detect a friendly in their area of effect. Of the top of my head GURPS, Shadowrun, Cyberpunk 2020, and even the 40k RPG all have technology that prevent weapons from firing/detonating if a friendly is in the way. Considering nearly everyone in Infinity has a comlog or radio of some form an IFF would be trivial to implement.
