Willem, as you will see on many posts WX5 cannot generate a project from html files. If the original project is lost and cannot be recovered then it will be necessary to start again (although you will have the advantage that you merely have to copy and paste the content from the web back into a project).

For future reference, please visit step 5 export, export project frequently. If you are continuing with v13 you can manually rename the iwzip as required (in v17 this can be done on the fly) so you have a number of backups. These do not have to be kept on the same PC (I use filezilla and copy the latest to the host for safe keeping)