Wow that's a real loss as such a tree potentially must have provided a lot of nuts if it is anything like the ones we have here in North France .
I am surprised that it's being killed by honey fungus I had not come across this before I wonder if something else is/was stressing the tree to make it susceptible to such a common fungus .
As for global warming being to blame not so sure about that as Walnuts are a big crop in the south of France and it's a lot warmer there
As for a replacement .... I wonder about a fig , if it's in a sheltered spot fig are taxonomically very different to most other trees and thus might not be so susceptible .
Living in Anjou , France,
For the many not for the few
http://www.permies.com/t/80/31583/projects/Permie-Pennies-France#330873