That's interesting. I bought an 80-year-old Hornbeam bonsai that died three years after I bought it. When it started to look a bit sick (brown edges to curled leaves; dropping leaves etc ... and this was a well looked after tree) I took it out of its pot and planted it in a vegetable patch. This was recommended by the bonsai owner who I purchased the tree from who was having similar problems, but with different species amongst his very large collection. He seemed to think it was due to shock from the dramatic weather we were experiencing. But it completely died with no green in the cambium etc.
My sense is that it that the trees demise was not due to any mistreatment, but simply it has come to the end of its life! Which is what I'm trying to find out
Well, in theory there's no reason for a tree to die of old age, I think.
Not that I'm really an expert in the field, but my understanding is that trees start withering and die once they become too big, as the roots end up no longer being capable of keeping it alive as the foliage/mass/roots ratio becomes unbalanced, and/or the roots would have sucked all the nutrients from the patch of land they grow in/on.
That's one of the reasons why root pruning and refreshing soil is such an important part of bonsai maintenance: our trees are kept small and their roots thin and efficient, hence keeping the plant in balance.
That is: if kept in proper care for its entire life, a bonsai would largely outrun its siblings in the wild in terms of longevity...