I am going to make my statement based on the scenario, and not whether the said scenario is true or not.
1. The child was 12 years old, and really did not understand fully the consequences of his actions.
2. Yet, at the age of 18, when the child was of the majority, he did not seek out his father then to make amends.
3. He only sought out his father after his mother died, when he is 26 years old.
Considering those factors, what I get from the scenario is that the young man was probably being still supported financially by his mother and step-father. After the mother died that support dried up. His step father probably wanted him to grow up, but the mother kept coddling him stunting his maturity level. So now he is out on his own, and he decides he is going to seek out his biological dad for the support his mother use to give him (probably financial, maybe more).
So, no I don't think there is any need to see his estranged son. If his son had come to see him right when he turned 18, I would say yes. Since he waited until he was 26 and probably struggling and a bit desperate, I say he should not waste his time seeing him. His actions between 18 - 26 speaks volumes, and so there is no need to clear the air.