I read and listen widely and the Abraham material is one source of teachings that I have returned to over the years. I am also interested in criticism of any work I study but I have found no criticism of Abraham-Hicks to be particularly convincing.
For me what matters is the material- the teachings themselves. I never felt Jane Roberts death in 1985 cast any aspersions on her work with the Seth Material, for example. The material still speaks for itself and I never hold the life of the messenger as being the example of whether the work is valid or not. That measurement is my own experience and what I observe of the world around me.
The nature of this work is that it connects our inner and outer experience and because we only have access to our own inner experience we can only judge the validity of the work by looking at our own life and inner world. Other people's experiences are irrelevant in this regard because we don't have access to their inner experience to judge its relationship to their outer manifestations.
Jerry's death and his use of chemotherapy near the end doesn't surprise me. Sure, it reflects a lack of faith in his ability to heal himself but when you are desperate most will turn to outside help and may even use treatments they previously rejected. This says nothing about the validity of the teachings, it just tells us about human nature and the nature of human conditioning.