Why does my unneutered cat roam for days? Will he become feral?

I see that Bagpuss isn't neutered. He's likely roaming for females to mate with, which is why he's disappearing for days at a time. It could also be that there is another home feeding him as well, and he's been staying there. To cut down on roaming behavior, I would have him neutered. He's a domesticated cat used to being handled, so he won't become feral by being around feral cats, but because he isn't neutered, he could get into fights with them over females and territory. After you have him neutered, you can keep him indoors all the time, and set up a litter box for him inside. That will keep him safe from the feral cats and home all the time. It's perfectly find to make Bagpuss an indoor only cat. Many people do it, and cats are perfectly happy with that arrangement. I have four indoor only cats, and they are happy :-)