You can't, because you can continue to use your device without a Facebook account for two years... which just so happens to be the statutory warranty period in the EU.
I'm in the same position as you, and from what I can tell we should be fine, though we may have to put up with some nagging from the damned Oculus store.
> [Re: 20203] If you choose not to merge your accounts at that time, you can continue using your device, but full functionality will require a Facebook account.
Which I read as "you won't be able to use the store anymore or receive driver/software updates for Oculus". I'm ok with that. By 2025 I'll either not be doing any VR or will want a new rig anyway.
I purchased these devices with the promise that I would not need a Facebook account, and I do not have one..