What did white southerners fear if slavery ended in south?

A lot of the people that feared slavery was going to end was farmers and plantation owners. They used slaves to do their work at the farms or at the plantation. So they feared they wouldn't have anyone but themselves to do the work.

Due to Union measures such as the Confiscation Acts and Emancipation Proclamation in 1863, the war effectively ended slavery, even before ratification of the Thirteenth Amendment in December 1865 formally ended the legal institution throughout the United States.