Even if you don't do anything, you can leave the account unused. I'll tell you what, you aren't the only one who leaves the account, I know many people who left their accounts unused in the forums and nothing happened. I was in another forum where there's an open source community that I registered about 7 years ago, I've come sometime and nothing happened.
To be banned, you should have become one of the guys who make drama or any breach against the community and with very bad behavior.
It isn't convenient for you to be a banned user, since there is a rule that will prevent you: "Ban evasion".
Think about it: What if you go back and need to ask something, collaborate or talk to people someday?
Forget getting banned, doesn't make sense. Leave the account and do what you want, feel free.
Doesn't matter if you don't use the account, nothing will happen.