Back in the early 70's there was a game ranch near Chelsea Michigan; and someone cut a hole in the fence and let out some russian boars and sows.
I remember because I was bird hunting and they ran off my dogs; and for a few minutes I stood real still..
Those things get big ! There were a bunch of piglets too.
I think all those got dead in short order; or were recaptured.
Wouldn't surprise me if someone let some pigs loose or some got away. But in Michigan- well its the home of 50,000 recipes for barbecue sauces; I doubt they will last long if they are there