According to Wikipedia feral cats can live up to 8 years or so with a median of 4.7 years. Assuming the cat was released young, was healthy and took to hunting quickly it could live up to 7 or 8 years but is more likely to live 4 years.
The average is likely to be less if you factor in older cats, cats that don’t take to hunting quickly etc.
There is a basic misunderstanding here. Cats are not domesticated. They domesticated us. Dogs are certainly domesticated, but cats are still wild animals.
My thirteen year old female, Cammie, isn’t the sharpest tool in the box around the house, she’s the one who lies down on a discarded plate and gets gravy all over her. Outside is a different matter, she has some excellent cat skills, she’s just poor at the cat human interface. She’s a prodigious hunter of mice, however it took until she was six years old to find out she could eat them. After a few minutes of horrid crunching she went straight out, caught another one and ate half of that too. Once the novelty wore off she decided she preferred cat food and hasn’t bothered to eat one since.
Last year, following a thyroid operation, she decided she hated us and went virtually feral for the summer. She did come in for food but clearly had no trouble finding outdoor shelter. While this was in an urban setting I think there are still a good amount of hideaways out in the woods for a small animal and being able to climb helps when it comes to getting away from predators. They are resourceful animals I’ve even heard about a colony of ferals in Antarctica who lived in penguin burrows.
So I think Cammie could feed herself and find shelter in summer but the winter would be her undoing. She gave up all that feral nonsense with the first real autumn storm last year and quickly remembered how much she liked snuggling with us on the bed (she is a ridiculous animal to have stayed away so long).