According to Wikipedia, the population numbered around 60 individuals at its peak in 1975; and as of September 2017, sightings were still being made in the area.
Wikipedia lists several other places, in the UK and overseas, where wallabies have bred successfully after being introduced either deliberately or accidentally. These include the Isle of Man; Inchconnachan (an island in Loch Lomond); near Teignmouth, in Devon; and the Ashdown Forest, in East Sussex.
© Haydn Thompson 2020