Default isn’t possible because it implies the notification state is set to your default in your preferences, and that’s not true.
“Not Tracked” is a bit of a non-statement with regards to what notifications actually occur. There are notifications in the typical state for quotes, @name mentions, and direct replies.
“Regular” conflicts with the user trust level of the same name
That leaves Normal. So the standard, typical topic notification state is now
Normal
You will be notified if someone mentions your @name or replies to you.
But doesn’t “tracking” mean that Discourse lists the topic in https://meta.discourse.org/unread? I mean, that’s the only difference between the current “Normal” and “Tracking” states (that I know of at least).
I still favor “Not Tracking” because, as @jspautsch said:
Okay, I understand what you mean. “Not Tracking” could also mean “Watching”, although your example isn’t the because because, by conventional definition, sanity and insanity are binary (i.e. there is no in-between or beyond).