What would happen? The Constitution would never get ratified. The provision for abolishing the slave trade was not that. What it was was a guarantee that it would be EVEN CONSIDERED until then. And they knew that they'd very likely have to move on that eventually, given the way Britain was moving towards abolitionism, and the RN command of the sea.
Err... No... Not exactly.
In the Trail of Tears, the US government didn't provide wagons or food or encampments, as far as I know. If they didn't do it for the "Civilized" Indians (members of the 5 Civilized Tribes), why would they do it for "uncivilized" blacks?
Still, the cost of rounding up that many people, providing armed escorts to force them to the coast, and providing shipping, all that would still be prohibitive. The US government had an INCREDIBLY small budget at that point.
Actually when Liberia was colonized they had to be continually supplied by ships for quite a while because the colonists didn't know how to live in Africa as Africa is quite different from the American South. They were given supplies, if they weren't they would have rapidly died out and that isn't what happened. In fact the American settlers pushed aside the natives and they couldn't have done that if they were starving on the shores of Liberia. Liberia is still dominated by African-American settler descendants .