> what license is fandom content under?

Generally, CC BY-SA https://www.fandom.com/licensing

> can an independent entity scrape it and start over?

Sure. The difficult part is migrating the community and competing in search results. Fandom can and does fight efforts to direct people from fandom-hosted wikis to elsewhere. See this other sub-thread: https://news.ycombinator.com/item?id=40711726