I actually watched a documentary on it a couple years ago. They were experimenting with different sauces, and forgot one vat for a while.There is no clear and known link between garum and Worchestershire sauce, which is produced very differently from garum.
Worchestershire sauce was created by, you guessed it, John Lea and William Perrins, and commercialized in 1837. Where they got the recipe is unknown, but they claimed various inspirations from India and Asia.
They eventually found it again, opened the vat, and tasted it. They did not die; it became Worcestershire sauce.