I had a similar problem and found a way to rebuild a project fairly quickly. I had compiled html5 files and a project from an earlier release.
This what I did:
- Create a new project. Give it the same name as the lost project.
- Import the .htm topic files into the new project.
- Copy the files containing the index (*.hhk), TOC (*.hhc) and glossary (*.glo) from the project of the old version into the new project.
- Use the Broken Links report to find and fix broken links.
- Compare the TOC in the new project with the TOC of the webhelp files. If you find any differences between them, manually change the TOC in the new project to make the TOC of the webhelp files.
If you don't have an old version, you will need to rebuild the TOC manually to match the TOC of the webhelp files. The Index Wizard is a quick way to build an acceptable index. Glossary entries can be created quickly by manually adding a new glossary term in the new project , opening the webhelp files, and copy-and-pasting the definition from the webhelp into the new project.