The html files can be served directly from the project file structure by navigating to them. This way you will not need to create any pages in Sitefinity. Note that if you, however, create a page or register another route in Sitefinity it will override them - they will not be accessible directly by Url.
Another option is to create redirect pages for each html page but this can cause a lot of redirects.
Do you want to have your say in the Sitefinity development roadmap? Do you want to know when a feature you requested is added or when a bug fixed? Explore the Telerik Sitefinity CMS Ideas&Feedback Portal
and vote to affect the priority of the items