Well, as I already stated, I don’t know why this particular thread was removed at the system level. I don’t have access to that information. I haven’t seen this happen before.
While the thread is unlisted, are you still able to see your responses listed under your profile under Activity > Replies ?
The FAQ and TOS are linked from the site homepage – and your menu bar, click the three = and click FAQ – from there you can further click Terms
As a community norm, we discourage deleting of questions or of question threads by users. If the thread has already had substantial responses from community members then we normally reverse the delete and lock the thread so that community responses stay visible and are not lost. I have done this many times in the last few months. There has been a long-running conversation about documenting these norms in a FAQ – it hasn’t been posted yet.