Reddit could survive with nothing but bots posting AI generated drivel and memes, and more bots endlessly responding with variations on "This," "Don't threaten me with a good time" and "That's what she said."
Just so long as the zombies have enough "content" to scroll through, inertia alone will keep it going.
The problem is that bots don't provide good content, specially not when the output of a bot is used as input of another. (This is called "model collapse" when it happens on the training stage, but you're bound to see the same in output-input chains)