I would say that the tree is dead. If a plant hasn't leafed out by June 1, I
would not expect it to. And that, in and of itself, is waiting a long while.
Most trees have begun leafing out in April and May if not before. A fast
death like you are describing could be from lightening, injury or chemical.
Most diseases make the tree weaker and weaker before death, but something
drastic, such as the above, or construction, grade changes, etc. can cause
trees to go. At this state, I would cut your losses, remove the tree and see
if in that process you can get a clue as to what caused it.
(August) What would cause a very large healthy gum tree ( the kind that drops
gum balls) to suddenly, after one winter, appear dead? Last summer it was leafed
out fully as it does each year, it also accumulated many gum balls as usual.
When fall came it dropped everything as usual. When this spring came it failed
to produce any green leaves at all and appears to be dead. If it is dead I will
need to remove it because it's close to the house. Is it dead or not ? Should I
give it another season ? How could it die just over the winter months after
being so healthy last year ? There are many other gums nearby that are fine.