Unlinking accounts will do nothing.

Even logging in with a non-linked Oculus account, still involves making a direct call to the Facebook graph api, that exists under the Facebook domain name.

You require full, unrestricted network access to Facebook, regardless the nature of the account used on the headset.

Any restriction of Facebook, will eventually propagate to Oculus use. But if you never connect the hardware to a network again, it will work till the authentication cookie eventually expires and requires a refresh. So it will eventually brick regardless, the only question is how long that takes, which becomes a question of how long the token expiry time was set for, by Facebook.