Perhaps the absoluteness of the act of writing, in effect, his own elegy--and the absoluteness of his inability to answer his critics afterward--curiously mellowed him.
He was mellowed by being unable to answer critics. 
mnli hypothesis: He was mellowed by being unable to answer critics.  premise: Perhaps the absoluteness of the act of writing, in effect, his own elegy--and the absoluteness of his inability to answer his critics afterward--curiously mellowed him.