It's up to you on how you interpret it since author said that wether they went outside or stayed inside, they'll always be together
which is tbh, in my mind, kinda sad cuz I'm so sure that if one dies the other will follow, I would think that they stayed in since the black lion wants to live as long as he can living with his mate but then again, I would think they went outside since the sevral cat wanted to show the black lion the outside which he has never seen and I can also see the cat's imagination about them walking outside, so like I try not to think about it since I know that they'll be happy and it's a novel in a novel which confused the heck out of me but I'm just glad they're always be together (=・ω・=)
Can someone explain pls... What happened to the black and several cat after they dig? Did they go to the outsider world or comeback to the protected zone, i want to know your Perspective guys