You should have a .h or .hh file. You can import that file into RoboHelp:
The downside of this method is that you have the map id's but you lose the link to the topics.
Do you know how the map id's and links to topics are stored in webworks? I'm not familiar with Webworks, but if they save that information in topics or in some control file, it will be relatively easy to create a script to migrate everything automatically.