ShiroKuro so an account could literally be canceled for getting a few down votes? That’s seems awfully harsh!
No, it doesn't happen. For example, user dwimback worked hard to get negative comment karma! He got as far as -99,000 or so, and then reddit decided to cap the negative score at -100.
You can get yourself banned from Reddit by the admins if you really go crazy, but for normal people it's unlikely, and the worst that happens is that a mod, at their whim, bans you from their subreddit. If that happens, you are still free to roam the others.
@Player1 , The top mod of r/pianolearning is nazgul_123. It's been a while, but I remember him as being a reasonable guy, and not one to ban on a whim. I'm sure you're safe.