As far as I understand, it’s not so much where a company/business/organisation is based but rather if that organisation, regardless of location, conducts any business inside the EU, then it has to abide by EU competition law.
Yes. If fifa held a competition in the us they would have to abide by us law not eu law (in regards to that competition). But as both uefa and fifa are based in switerland (which uses eu law) if the ecj ordered their break up, unless they moved they'd be broken up.