AppViews already had to archive whatever data from the network they cared about. The change just means that an AppView won't be able to infinitely backfill from any relay, you either need to find a relay that archives all the data you want and backfill from that relay, or you'll need to backfill by querying pds's directly. Or you could just not backfill at all, your AppView can do whatever it wants to really. Clients always talk to an AppView to get information about the network, the AppView manages the building of reverse links, the relay doesn't care about the hydrated state of the network, its just a stream of events which occur on the atproto network.