It would have been fine as long as the yankees would have left us alone. Slavery would have failed anyway. There were many many antislavery southerners. It would have been voted out eventually.
I doubt it would have died from a vote. The Mason Dixon Line would have continually crept south as people discovered that it was cheaper to pay people and send them away for the night, than to house, clothe, and feed them; and then care for them in their old age. It's not like there weren't slaves in New York, or that lots of people died to free them.
ML/NJ