Well, you gave us some pics of failure at the stem there...and certainly looked like
Ganoderma sp in the last pic too.
By the time you have lost so much functional tissue strength to lead to failure like that you would certainly expect to have many VTA signals to alert you of imminent doom. That tree of yours I would describe as fecked...meaning so clearly beyond the point of recovery that even someone who has no Arb training or understanding would recognise there is a major problem..we've all seen fecked trees.
Here are some of the VTA signals i would classify as being in the realm of being fecked.....
The production of roots from under the bark (lifting off and dead) in a sheet extending beyond 20% of the circumference of the stem
The dieback of over 50% of the canopy of the tree
Stem cankers evident in current and past fruiting bodies around the entire circumference of the stem.
Close up
Same species of Euc, different canker through the base of the tree
Closer look
The point being when you have these sorts of slap you in the face indicators, if there is any significant target present removal has to be the number one option.