Right now the schedule will build just fine, even if block there are dangling block references. This causes things to vomit and die in the PlaylistManager. Fix this.
Or we could featurize this and just have the ability to load chunks of schedules independantly of the main schedule. Block ptrs get resolved later. That way, people could define their own shows as xml snippets <Block>...</Block> and then merge these on the fly with scheudle?