Rules Reference Guide, page 5, Attacks wrote:
When a figure performs an attack, it resolves the following steps:
1. Declare Target: Based upon its attack type ((melee) or (ranged)), the figure
performing the attack (referred to as the attacker) declares one
eligible target for the attack (referred to as the target).
- For a melee attack (melee), an eligible target is any hostile figure
adjacent to the attacker. For a ranged attack (ranged), an eligible
target is any hostile figure within line of sight of the attacker.
You can't even get out of step 1 without a hostile figure in line of sight.
As to your second question:
RRG, page 6, Attacks wrote:
The keyword abilities Blast and Cleave, and any keyword that
causes a condition, all require the target of the attack to suffer
one or more (damage) to trigger.
so.. some stuff can trigger off of a miss (Healing, mostly), but specifically not Blast or Cleave or anyhing that applies a Condition (including Focus for yourself or an ally).