It's just a hypothetical I don't think it will come to it, but wondering why that would that lead to antitrust case? My knowledge of law is non-existent. I thought antitrust suits are because of getting into a monopoly position. Are you arguing that such an action would leave them open to claims of monopoly? Forfeiting services might be seen as a form of abuse, but isn't it sort of opposite of an antitrust by forfeiting your monopoly / strong market position?
You're leveraging your dominance in some sectors in order to gain advantage in another sector. That's what they got Microsoft for. Also can't imagine countries bowing down to these kinds of tactics anyway.
Deciding that it's no longer worthwhile to provide services to everyone in a country is not leveraging your dominance. It's giving up. They can't force Google to operate in Australia.