Hmmm,
b - YES- P.16 "Assaulting a unit inside Cover: Assaulting a unit inside cover is a much more dangerous task and often fatal to both sides involved. An Assault action against a unit in cover is therefore fought simultaneously by both sides.
Fight simultaneous Close Combat: Roll Close Combat Dice for the unit participating that has at least one enemy unit within their CR. Note that the assaulted unit inside Cover only rolls one Damage Die, no matter how many Close Combat Die it normally has. Note that this allows the unit in cover to fight back even though it is not taking an action!"
a - NO!
Assaulting units attacks. That's it. No free strike or so!
If the defender survives, he may strike back later once activated by performing a Close Combat action!