"Your identity should not be coupled with the moderation policy of whichever platform you host your social graph on"Yes it should. This solves the moderation problem which the author talks about. You go to the instance with which you have the greatest affinity. Affinity groups don't usually need to do much internal policing, and it's the extremely arbitrary use of moderation powers which is one of the major problems driving users to leave the silos.
On guarantees of continuation of service on the internet there have never been any such guarantees. In siloland, such as Facebook, you can have your account or group censored on a whim without explanation or any possibility of data recovery. No guarantees of continued service there either. They simply do not care about individual users or sometimes even sizeable groups. Ultimately the only services you can trust are those run by people with whom you have some degree of affinity.