Interestingly, both the North and South, as separate countries, would tend towards a pro-British position. The Deep South was economically pro-Britain, but supported Jefferson becaue he was a Southerner and they liked him domestically. Without the Deep South, the Jeffersonians are screwed. Federalists (pro-Britain) rule up North. In the South, meanwhile, a Jefferson-esque domestic policy prevails, but in foreign policy, they'll be pro-Britain. As such, the man most likely to hypothetically be inclined to force unionism via war (Hamilton) will actually be jumping for joy that the Deep South stayed out of his precious union: it really screwed Jefferson over!
In the long run, slavery is probably dead sooner in the North. The Southern country, meanwhile, will hace little internal opposition to slavery. This means it never becomes such a hot iron issue, and you may well prevent a lot of the bizarre extremist justifications of slavery we saw in OTL. In the end, it'll probably be abolished there without a big war, although probably later than in OTL. Here, we should really think of Brazil's situation in OTL.
With regards to slavery, I would assume that it'd be ended by the 1830s. The Constitution was ratified in 1788 and the slave trade was ended in 1808 - let's say slavery is completely phased out by 1828. New York ended it completely in 1827 OTL.
With regards to Jefferson and domestic policy, there's still going to be a constituency for him. He won PA OTL in 1796. He won PA and NY in 1800. In 1804 he won every state but DE and CT. Odds are that Adams wins in 1800 TTL but Burr or Madison will win the election of 1804. In 1808 and 1812, if you subtract the three states that aren't part of the country here, you still have Democratic victories over the Federalists. Once Ohio and Louisiana are admitted, I don't think the Federalists will be able to win elections anymore.
The Naturalization Act of 1798 and the Alien and Sedition Acts were what really screwed the Federalists. And it isn't as if SC, NC, and GA not being in the country affects congressional elections that much 1800 onwards. Prior to 1800 there's only one election that the Democrats took OTL that the Federalists would win here, and one other where it'd be a draw rather than a Democratic win.
- In 1780 the Pro-Administration Party would still have a sizable majority, as per OTL.
- In 1790 the Pro-Administration Party would still have a sizable majority, as per OTL.
- in 1792 the Pro-Administration Party would still have a sizable majority, whereas OTL the Anti-Administration Party won.
- In 1794 the Democrats and Republicans would have the same number of seats (44-44).
- In 1796 the Federalist Party would still have a sizable majority, as per OTL.
- In 1798 the Federalist Party would still have a sizable majority, as per OTL.
- In 1800 the House was 68 Democrat and 38 Federalist.
- Without the three states, it's 57 Democrat and 31 Federalist.
- In 1802 the House was 103 Democrat and 39 Federalist.
- Without the three states, it's 82 Democrat and 28 Federalist.
- In 1804 the House was 114 Democrat and 28 Federalist.
- Without the three states, it's 90 Democrat and 28 Federalist.
- In 1806 the House was 116 Democrat and 26 Federalist.
- Without the three states, it's 93 Democrat and 25 Federalist.
- In 1808 the House was 94 Democrat and 48 Federalist.
- Without the three states, it's 73 Democrat and 45 Federalist.
- In 1810 the House was 107 Democrat and and 36 Federalist.
- Without the three states, it's 85 Democrat and 34 Federalist.
- In 1812 the House was 114 Democrat and 68 Federalist.
- Without the three states, it's 89 Democrat and 65 Federalist.
- They made the House larger after the 1810 Census.
The Senate meanwhile remained Pro-Administration/Federalist until 1802 OTL, and the 1802 Senate elections ended with 22 Democrats and 9 Federalists. In 1804 it was 25 to 6 (27 to 6 after admitting Ohio). In 1806 it was 28 to 6. The Democrats would continue to have double or triple or quadruple the number of Federalist Senators going forward.