So many issues here: how old is he, how complex are the health issues, is he even able to travel, does he have family in the UK to support him when he arrives, which part of the UK will he be returning to (NHS access seems to vary considerably according to location), is it even financially viable at this stage of life, ie. what is his source of income in Austalia and will that be enough to support him in the UK?
(I don't know if you can change the thread topic to something more appropriate such as "Aged Person Returning to UK" but I think it would receive more responses than the current heading).