Absolutely. I discourage cyclic, but dag is ok. It can be hard to write a downstream chapter (and keep the plot consistent) when there are two upstream paths, so we don't do it a lot, but we have a few examples. I think in our current story of about 110 chapters, we have three crosslinks, and two of them have a major impact on the story. I wrote a pretty snazzy react/cytoscape thing to visualize and explore the maps.