How to force disconnection for case you're on public space ?
This is not possible with Persona's current API.
However, we do have an experimental / undocumented option, experimental_forceAuthentication: true, which forces re-provisioning when passed to navigator.id.request({ ... }).
As with all things experimental, please do not rely on this, expect it to work, or expect it not to break your site in the future.
Still, if you do try it out, please provide feedback on the dev-identity mailing list regarding your use case and whether or not this would be a suitable resolution.