How does Dunstan respond to Denyse’s request that he write Boy’s official life? What are the reasons Dunstan doesn’t write it?

Dunstan puts her off by saying he would think about it. He doesn't write it, Of course I did not write it. The heart attack I had a few days later gave me an excellent excuse for keeping free of anything I didn’t want to do. And how would I have written a life of Boy that would have satisfied me and yet saved me from murder at the hands of Denyse?