Am I right in seeing that the lean is away from the house? What is it leaning into? Can you tell the portion of the circumference at the base which is killed? Of course, the amount of sound wood to the outside is more important than the volume of decay on the inside, but my concern here is how much necrosis is present around the base, not just the thickness of the band of wood to the outside. Does the crown look good with good branch extension? This is where you practicing arborists have tougher decisions to make than I do. If tree preservation is the top priority, I'd go with drill exterior. If safety/peace of mind was top priority, I'd consider firewood. But that's just me, you see more of the success and failures than I do.
As for the amount of bracket fungus you removed, I have attached a 1970 paper from my research grandfather, F.A. Wolf. This is a later article from him, he was E.S. Luttrell's major professor at Duke, who in turn was mine at University of Georgia. At the risk of losing anyone who might be reading, Wolf studied with G.F. Atkinson who was a student of W.R. Dudley's at Cornell, the latter whom went to Strasbourg to study with A. De Bary, father of the germ theory and modern mycology. De Bary is remembered mostly now as being also the major professor of Louis Pasteur. Pasteur had good industrial and business connections through his work with bacteria, but most of the principles he "discovered" were previous identified and published by de Bary.
