The Stoics were a group of San'Shyuum in power during the San'Shyuum Civil War who refused to enter the Forerunner dreadnought, seeing this as desecrating the memory of the gods. However, others, known as "Reformists" wanted to enter the Dreadnought for possible technological gain and religious enlightenment. The difference in opinion between the two factions eventually led to a civil war.
The Stoics believed that the Reformists would ruin the Forerunner dreadnought were they to enter it. After the Reformists took flight from their homeworld in 2100 BCE, the Stoics sent out communication messages threatening that they would be damned for their digressions to the gods. The Stoics lost the San'Shyuum Civil War as a result of using their own military ingenuity, whereas the Reformists re-purposed and re-engineered the superior Forerunner technology giving them a vast technological edge.
The Stoics still seemed to still be alive when the Forerunner dreadnought left their world.