Actually many states were moving toward a free society. Manumission had become common in wills, so much so that special laws were passed to cover the topic. In fact, as shown by the post civil war era, it was more economical to hire free workers and pay them a pittance than to own slaves.But since you asked, do you really think the south would have gave up their slaves? They could work in the summers, withstanding the heat, most were also immune to malaria, and they were cheap. There is no way the south would have sold their slaves, most of their economy was based on slave labor.
Slavery is generally only profitable when there exists a labor shortage. When there is a surplus, hiring labor is far cheaper than owning slaves.
Labor only needs be paid on the days they work. Slaves must be fed, housed, clothed and given care all the time, even the off season.
There is no capital investment in labor. Slaves must be purchased, or raised from infancy - both cost money.
Lazy laborers can be dismissed. Lazy slaves can only be whipped.
A laborer who runs away takes no capital value with him. A slave who runs away costs money.
Only the most infantile analysis suggests slavery is universally profitable.
Why would they want to sell something they had invested so much time and money in?
it was already on it way out, some people here have already talked about the new influx of cheap labor as well as technological advances. most of the owners would have loved to get a decent sum of money per slave and be done with it.