It seems like since she knows a reliable food source, she'd be back looking for food if she had her kittens. But I don't know anything about how pregnant cats behave. Hopefully, someone will have more information for you. I took care of a stray for 6 years, and he disappeared in September. In his case, I'm almost certain he died, but not knowing for sure is so hard. I hope your feral comes back, with our without kittens!