So, I'm trying to get the mod to load the whole world while in preview mode, but it is not happening.
I've loaded every chunk of the world while recording and the preview mod continues to un-render chunks after 5 chunks away. This is super important for a good quality video that I am attempting to create.
The Replay Mod does not force chunks to remain loaded once you have entered those chunks. If you move away from the chunk while recording, Minecraft would unload the chunk, and as a result the Replay Mod will no longer record what is going on in that chunk because no packets/data are being exchanged between the server and client.
So to answer your question, you can unfortunately not keep a whole world loaded.