I know a guy who had two contracts like this. He did the work himself, but then they both kept him on $3k monthly retainers to just be available in case anything breaks. He didn't work for about a decade, and then when the contracts ended, all his skills were a decade out of date and he couldn't get work. But, he had saved up, bought a house which 4x'd in value, and is only just starting to worry about money another 10 years later.