Mark McShane, 40, was left unable to recognise his own children after the attack in Letterkenny, for which two men were jailed for five years.
The Derry man later had part of his brain removed.
His brother John said he now lived on his own and struggled to survive everyday.
“He still is pretty much brain-damaged and possibly is going to be for the rest of his life,” John told BBC Radio Foyle.
“Mark finds it pretty difficult to survive on his own.
“All the care that Mark gets is provided by his family, because as far as all those outside agencies are concerned, they seem to have walked away from him.
“Mark refused to go to a clinic on one or two occasions and it seems to be that no one ever contacted Mark to see if he wanted to come back.
“It’s a lot of strain on my mother; it’s a lot of strain on all of us because every day somebody has to do something for Mark, take him somewhere, cook for him, clean for him. He exists, that’s it, but as far as his mental state is concerned, he would be pretty much childish.”
He said he would like to see the brain injury clinic do more to help Mark, and he said the Housing Executive could do more to improve his accommodation.
The Western Health and Social Care Trust said it could not comment on an individual case but that Mark’s family could raise concerns about his treatment directly with staff or through its complaints system: the Patients’ Advocate Office.
The statement added: “The Acquired Brain Injury Service is working within the agreed regional standards and quality indicators on acquired brain injuries. These acknowledge brain injury is a lifelong condition but state that ‘the active participation and engagement of people with a brain injury is central to any rehabilitation process’.”
The Housing Executive said it had received a report about a cylinder leaking at Mark’s address and its contractor called at the property twice, but could not gain access. A spokesperson said a maintenance officer would call at the property on August 8 to carry out an inspection and any items found to be defective or in need of repair would be addressed.
Two Donegal men are serving five-year sentences for their part in the attack.