I don't see why the tunnel workers would have to be made either rich or dead. They need not know anything about where Guzman is now, so why would it matter if they talked? Doing so would get them in trouble with the authorities, and would likely lead to them then being killed by someone hired by Guzman, so it would probably not be smart for any of them to blab about this.
"A wise man ... proportions his belief to the evidence."
— David Hume, An Enquiry Concerning Human Understanding, Section X, Part I.
