They don't fire for the entire battle, they fire for the round they are destroyed in. After that round ends, they are removed from the battle. This is designed to simulate simultaneous firing, rather than sequential.
Example (without numbers for simplicity): 4 Yor ships attacking 4 Terran ships of slightly lower tech:
Old method (DL and first round of a combat in DA or TA where the attacker has Super Warrior ability)
All 4 Yor ships fire, destroying one Terran ship and damaging a second. The three surviving Terrans fire back, destroying 1 Yor ship. In the second round of combat, the 3 surviving Yor ships destroy 1 Terran ship and damage another. The 2 surviving Terrans damage a Yor ship. Third round of combat, the 3 surviving Yor ships destroy both remaining Terrans.
New method (DA and TA, except in special case mentioned)
All 4 Yor ships fire, destroying one Terran ship and damaging a second. All four Terrans fire back (since this is intended to be simultaneous firing, the destroyed ship hasn't been killed yet), destroying one Yor ship and damaging a second. Second round, the 3 Yor ships destroy the damaged Terran ship and hurt another; the 3 Terrans returning fire does the same. Third round, the Yor finish the Terrans, and the Terrans destroy the damaged ship, with maybe some damage on the last ship.
The new method takes away the massive advantage the attacker had in DL, making closely matched fleets end in closely matched condition. With the DL system, even greatly inferior fleets could do far higher proportional damage if they were attacking.
