[squeaky-clean]

Just have your bot log off and "sleep" randomly for 4-10 hours every night, and log off for 15 minutes every few hours during the day. If you ever get a private message, have your system play a beep (or ping you on IRC then/Discord nowadays).

As for not talking to anyone, a surprising amount of people play MMOs just like that, so it's not really atypical for a player to never communicate. Runescape even has an account choice, "Ironman Mode", where you have to play the game self-sufficiently, and can't trade with or rely on any other players. You can still chat with other players if you want, but you don't have to.

[Natsu]

I've seen people try that, but the admins just sit there quietly watching them loop for an hour or something, then note how long it takes them to respond to a simple hello.

Or in some games, they can send messages in a way that a human would see, but not a bot who expects the messages to come over chat. For example, waving a sign in front of the character's face with a message or whatever. It helps that the admins can also hide from normal presence detection, even though they're visible on the bot's screen, visually.

I've literally watched admins ban a bot using these precise countermeasures. The trick is to always keep giving them new things they haven't thought of to adapt to.