She struggled to get neighbouring residents to evacuate and that caused a delay in her phoning emergency services, the coroner said.
The support worker shouldn't have been the only one working, Coroner Scott added.
In his finding, the coroner said overnight staffing numbers should be increased to two, while there needed to be an ongoing education programme, including fire drills that involve both clients and staff.
The 10-unit facility was built in 2010 but there was no legal requirement for sprinklers to be installed.
The coroner has raised the issue with the care facility's operators, a charitable trust called Whatever It Takes (WIT), but they say estimates suggest the installation of such a sprinkler system would be $100,000, and much too cost prohibitive.
He urged them to do what they could to install sprinklers or else warn clients and/or their welfare guardians that there was no such system, and also refuse to accept clients who were smokers.
"Although I accept that there is no legal requirement to install sprinklers, I think that it is highly desirable in a complex of this nature that they are installed," Coroner Scott said.
"It is probably reasonable to conclude that had sprinklers been installed then they probably would have operated to extinguish the fire in its early stages and it is highly probable that Gavin would have survived."
WIT general manager Caroline Lampp today said that all of the coroner's recommendations have been acted upon.
Fire drills, involving both staff and clients, are being carried out every three months and alongside the fire brigade twice a year.
"We're always trying to review what we do and make things better," Ms. Lampp said.
"But with this particular client, I don't know if any amount of those things wouldn't changed much, to be honest. He was a particularly difficult client to have, and that's why WIT had him, because no one else would."
They are also further investigating the "complicated process" of installing sprinklers, she said.
Mr Hall, who had trained and worked as a linesman for five years, suffered serious injuries, including a brain in jury, in a motorbike accident in 1978.
Since then, he was confined to a wheelchair and suffered ongoing mental health issues, though despite refusing medication, his psychotic symptoms were regarded as being at a manageable level, the coroner notes.
Coroner Scott concluded that he died from the effects of the fire, in particular, from smoke inhalation and carbon monoxide blood saturation.