From a fairness standpoint, yes. There could be some people who are advertising a company outside of the signature campaign, for example because they have an ownership stake in the company, or work for the company in a role that benefits when the company has increased sales/volume.
I don't know if I agree that it is fair to allow someone to continue to advertise for a banned advertiser, simply because they have an increased personal stake in that advertiser. I might be misunderstanding your statement again, though, so please correct me if I'm wrong.
As far as I know there currently aren't any campaigns that are operating off-site, but admittedly this is not something I keep up with in any capacity. It would seem only banned advertisers would have any reason to do so, but I might be wrong about this. Regularly it is very easy to tell if someone is genuinely associated with a campaign, because campaign managers are extremely transparent with their spreadsheets and applications are normally public. Granted this isn't a rule, but it would seem an easy guideline to adhere to if you want to run a legitimate campaign.
I'm mostly thinking out-loud, and I see where you're coming from, but there seems to be applicable answers to these questions.
That is still a de-facto license.
I feel like we're playing word-games at this point.
If there were nothing resembling a "license" then there would be no enforcement of any guidelines and we'd be where we currently are (or worse).