After Veilguard, Manfred continues to learn and grow just as he did before, as a being in the living world and also as a mage.
And he starts to gain more independence, and to learn from teachers apart from Emmrich.
And, eventually, he becomes a full member of the Mourn Watch, and then a senior member.
And he takes on his own proteges, spirit and living, and teaches them everything he’s learned.
And, one day, Emmrich dies.
And Manfred, as his son, tends to his body and his grave with the same reverence for the honored dead that Emmrich taught him.
And as long as Manfred remains in the world, he carries on Emmrich’s legacy in his own actions and those of his endless chain of students, each one given the love and care and support that were the foundational gifts his father gave him.
This, too, is immortality.