What would most likely have happened to the Roman economy if the slaves were suddenly freed?

Slavery in ancient Rome played an important role in society and the economy. Besides manual labor, slaves performed many domestic services, and might be employed at highly skilled jobs and professions. Accountants and physicians were often slaves. Slaves of Greek origin in particular might be highly educated. Unskilled slaves, or those sentenced to slavery as punishment, worked on farms, in mines, and at mills.

Roman mosaic from Dougga, Tunisia (2nd century AD): the two slaves carrying wine jars wear typical slave clothing and an amulet against the evil eye on a necklace; the slave boy to the left carries water and towels, and the one on the right a bough and a basket of flowers[1]

Captives in Rome, a nineteenth-century painting by Charles W. Bartlett
Slaves were considered property under Roman law and had no legal personhood. Most slaves would never be freed. Unlike Roman citizens, they could be subjected to corporal punishment, sexual exploitation (prostitutes were often slaves), torture and summary execution. Over time, however, slaves gained increased legal protection, including the right to file complaints against their masters.

A major source of slaves had been Roman military expansion during the Republic. The use of former enemy soldiers as slaves led perhaps inevitably to a series of en masse armed rebellions, the Servile Wars, the last of which was led by Spartacus. During the Pax Romana of the early Roman Empire (1st–2nd centuries AD), emphasis was placed on maintaining stability, and the lack of new territorial conquests dried up this supply line of human trafficking. To maintain an enslaved work force, increased legal restrictions on freeing slaves were put into place. Escaped slaves would be hunted down and returned (often for a reward). There were also many cases of poor people selling their children to richer neighbors as slaves in times of hardship.