It really depends on what the regulation is. If it's something to the effect of making a siloed company for AdWords that needs to offer FRAND terms to everyone, plus Alphabet is bared from doing its own ads, and has to contract it out, then AdWords Inc could gather more of the market and become even more dominant. This would still be a win, because the new, more dominant, advertising platform would not have any other businesses to anticompetitively promote. Maybe you would get competitors offering different terms, but that's probably wishful thinking.
A company that operates in a jurisdiction is regulatable by that jurisdiction. In this case, if Google weren't physically present, you sanction advertisers and local sites that use the ad service. In cases where there's no economic connection, the option is to force ISPs not to carry that traffic (and all the cat and mouse that entails).
Also, a lot of mobile carriers are international companies. In each country, they follow the local regulations. They have some economies of scale that may make it easier to compete with a network that's only in one country, but it depends on the size of that country how big the effect is.