In general what you have to do with any proprietary file format is find someone who has the program. Assuming it is a lady, you send her the file, she uploads it as a new data base, then downloads it as a GEDCOM and sends it back to you. She also either gloats over all the family secrets revealed or deletes the data.
You might ask the lady in the link how she did it. If it was as I suspect, she may still have the address of the person who has a copy of Generations. Genealogy.com technical support may offer the service, if they have taken over Generations.