How could he have died and where?
ah, where indeed?
I who have wandered into and returned alive from the curious regions he attempted and died to explore, have unfortunately never come across a single record or any remains or traces of those long lost but unforgotten braves.
Leichhardt originally started on his last sad venture with a party of eight, including one if not two native black boys.

Owing, however, to some disagreement, the whole party returned to the starting point, but being reorganised it started again with the same number of members.
There were about twenty head of bullocks broken in to carry pack-loads; this was an ordinary custom in those early days of Australian settlement.

Leichhardt also had two horses and five or six mules: this outfit was mostly contributed by the settlers who gave, some flour, some bullocks, some money, firearms, gear, etc., and some gave sheep and goats; he had about a hundred of the latter.

The packed bullocks were taken to supply the party with beef, in the meantime carrying the expedition stores.

The bullocks' pack-saddles were huge, ungainly frames of wood fastened with iron-work, rings, etc.
Shortly after the expedition made a second start, two or three of the members again seceded, and returned to the settlements, while Leichhardt and his remaining band pushed farther and farther to the west.
Although the eastern half of the continent is now inhabited, though thinly, no traces of any kind, except two or three branded trees in the valley of the Cooper, have ever been found.