It's back! Thank you. I wish Apple would have just given us a warning and we could make the decision for ourselves rather than automatically cutting it, saying there was a new version (a lie) and not telling us that reactivation was available. That was *not* nice Apple!
Just updated to Safari 12.0. When I reopened Safari, it said it was removing the AdGuard button because it is slowing things down and has an update. I couldn't find an update anywhere. The button in the lower right corner is still there.