I knew I shouldn't have used the word "never", although I was thinking that only "deleted" accounts would drop the total count. That's also a good point.

But it still seems unlikely that there will be a LOT or cases where the total number drops by a proportionately large number, unless something really bad happens (or there's some big initiative at some point to remove inactive or not accounts)

The more important stat - the one that people would be much more likely to be talking about seeing a "decline" in, in cases like this - is "active" users.