> could get rid of third party cookies tomorrow and not get sued out existence?

I don't think people abusing cookies have a standing as I see it. On what grounds, that their predatory business model is obsolete?

On the contrary, even if many web services are financed by ads, most customers of advertising just care about having the same possibilities to advertise their products. So a more healthy ad world would remain.

"Legal" advertising has eclipsed spam with its toxicity.