How long does it take for a cat to forget people/places?

My aunt was watching my cat for me (long story), and it was only supposed to be for a week or two. It has been almost a month, because I wasn’t able to get ahold of her. I didn’t want to harass her, since I know she was in the process of moving and working a night shifts, but she did finally get back to me.
She said that she can’t catch the cat… that he runs like a feral animal the second she walks into the room. He has always been skittish (we’ve had him for 6 years, since he was a kitten), but that is extreme even for him. I’m assuming that being taken out of his environment was just too much stress.

So… now my cat has been away from home for a month. Catching him is going to be even more traumatic, because he is already freaked out and that will just be another event on top of it. Is he going to remember us? Will he remember the other two cats? Is he going to know that this is “home” or will it be like bringing a brand new cat into the house for the first time?

I am so worried that he isn’t going to adjust, or that he will have forgotten that this is his home. All three cats have always gotten along beautifully, they are a little family, but will that be ruined now?