They certainly can survive on their own. I know this may sound harsh, but you would be giving them another chance at life -- probably a happy life if you were able to befriend them and feed them when you are there. Yes, they can become lunch for a coyote or loose dog, but ...
Two of my traps are currently lent out to friends trying to catch a few feral cats. At certain times of the year, various organizations around here provide free or very low cost neutering, along with rabies vaccinations. In this case, my friends will take the cats back home after they have been neutered.
The farm where I do my yoga lessons has a number of feral cats, many of which I've been able to befriend. The farm provides medical recovery services for horses. As a consequence, it gets lots of visits from veterinarians, who provide free cat/dog neutering on a somewhat regular basis at the farm. One of the ferals has been on this farm for 13 years. It will come up and rub my legs when it sees me, but I can't touch or pet it.
These particular ferals are fed regularly in a controlled area, but they still do their job of keeping the rodent population under control. If you do feed yours, it needs to be in a controlled area at a regular time. Otherwise, other critters, like raccoons, skunks, and possums can become an issue.
We have a very human-friendly Siberan Forest cat who we took in as a rescue cat a number of years ago. He is quite humorous. He is about the size of a Maine Coon Cat. He's made good friends with our UPS delivery guy, and jumps in the UPS truck when it arrives. He loves people. But, he will more than stand his ground with dogs or any feral/stray cats that come around. He's not very fond of snakes either. Yet, he will very gently and authoritatively help me get my guinea fowl and chickens back in the pen in the evenings. He and the guineas are protectors of the chickens.
Anyway, give it a try.
