I guess it's possible that it might be held to be, but it's by no means a given. (I don't know any English cases on that, but there may be US ones I'm not familiar with. All the cases of website terms I know are ones where the website owner wants to enforce against the user, so don't help, as AFAICS the courts only care whether the party seeking to enforce gave consideration (which they have: the service)).

But even if you succeed in that, it still might not help you. Seems to me that the effect of that would be to make the service a standing offer on Google's part. Analogy: a sign on a shack saying "Come in and take a biscuit if you view the advert on the wall". The consideration isn't in return for a promise to continue to provide services. If the shack owner removed the shack one day, you couldn't sue him for breach of contract.

Wheras if you've paid money for a service and they don't provide it, they're in breach, full stop. (Even if they claim you're in breach, they have to notify you and give you a reasonable time to cure it).

IANAL, and my consideration analysis might be completely wrong. But even if it is, I still strongly suspect it's not going to be easy to convince a court to hold Google in breach for stopping giving you a service you weren't paying for. If you're paying for a service, you're in a much more secure position.