No, you can't buy back your defeated heroes in Heroes of Might and Magic III, and you can't do it here either. We were talking about dismissing heroes, and you can do that both there and here. Read the rules carefully; is it really that difficult?!
That's not true! Let's read the rules again:
2.3. You can use a redeemed escaped/ransomed hero in battle on the day they escaped/were ransomed. You can redeem such a hero on the day of their escape/ransom;
you can only buy back and use your dismissed/defeated in battle hero on the day after their dismissal/death;
if a hero escapes/is ransomed/dies in battle during a turn transition, you can buy them back and use them immediately;
