Given their investment, both in chattel property and in ideology, combined with their petulance and pride, I totally agree with you - they would have hung on to the bitter end (just like they did).
The system would have stayed in place so long as cotton agriculture was profitable to the Southern planters. The only thing in the short term that would have ended chattel slavery, at least on the scale practiced in the South, would have been machines. The first practical cotton harvesting machine, built in the 20s, harvested the same amount of cotton as 60 field hands could pick in one day.
Had such a machine be available in the 1860s, slavery would have died out much faster.