They will have to satisfy regulators from all major regions where they want to operate. Non-compliance results financial, or criminal penalties or not being allowed to operate in EU.
In theory FB could just agree with EU that they will cease all operations in EU and leave in peace, but that would effectively kill FB over long term. Competitors would crush them. Imagine a mobile carrier who can't make calls to EU or email provider who can't sent or receive calls from EU. FB is in the same situation. It's a social network. Value for the users comes from connections.
Every international company negotiates some kind of deal if they want to stay international.
In theory FB could just agree with EU that they will cease all operations in EU and leave in peace, but that would effectively kill FB over long term. Competitors would crush them. Imagine a mobile carrier who can't make calls to EU or email provider who can't sent or receive calls from EU. FB is in the same situation. It's a social network. Value for the users comes from connections.
Every international company negotiates some kind of deal if they want to stay international.