I check my campaign threads, spreadsheets regularly, several times a day to ensure everything is in order. In a random week, I can miss the checking for one, two or a few days but that's exceptional.
I haven't seen this being an issue in the forum provided there is a good communication. I think Op believed he informed Royse777 about leaving the campaign, but he did it in a wrong way. You wrote that you are leaving a particular campaign that your post count as of when you made the post of leaving the campaign was 1000, then you removed the signature. Let's say the manager wasn't online and managed to come online after 12hrs, saw your post and noticed you are wearing another signature. How do you want the manager to believe that it was excat 1000 posts you made wearing the signature of your previous campaign?
The user removed the signature over a day before the campaign weeks ended. If that was one or two hours before the week ends and a post confirming of moving status then it's somehow considerable but out of 7 days missing over a day is not acceptable.
A member can mistakenly remove the signature but in a few hour times if he realize it was a mistake and if I trust the incident was true then I have no problem. It already happened with one of signature campaign participant in one of the campaign I managed. All these situations are looked at case by case, there are no certain defined book however it's always advised to read campaign rules. One of the important rule is as follows -
▶️ You are not allowed to change anything on the signature code, if found then you will be disqualified without prior notice.