Pat Young
Would agree with most of that but uncertain about the last. There is likely to be a strong revanchist element but I can also see significant counters to it for several reasons.
a) As you say the union/north/US has clearly lost a war, which will be an hell of a shock and the 1st time its clearly happened so there's no way of knowing how it will react. Plus while less bloodier than OTL as it could be nearly two years shorter its still a lot bloodier than anything the US has known before. As such while there will be elements who will argue for hurting the south in any way possible there will be others who want to avoid another costly war, which is a quite possible outcome from any such action and at least some of which will consider the 1861-63 conflict a stupid and unnecessary one.
Also while the defeat is unlikely to kill off American exceptionism its likely to weaken it and cause a degree of introspection, which is likely to involve looking for scapegoats for why the union lost the war. This could include the south for winning battle, European powers for stepping in, probably by recognising the south and breaking the blockade. Its also likely to include assorted internal groups, such as the copperheads/peace Democrats, the radical Republicans for pushing things too far, assorted minority elements including the Irish [especially after the draft riots if they still occur and especially if as is likely Britain is one of the main powers intervening to end the war], the Germans as I have read here some questions were raised about German migrants, the blacks - for 'starting' the entire mess and the British - for the reason mentioned above. This is going to cause a fair amount of internal tension for a while at least.
b) Since it was Lincoln and the Republicans that 'started' and the 'lost' the war there is likely to be issues there, both with some hostility towards the party as a whole and possible splits in the Party over whether to double up or moderate things. Assuming the peace is agreed sometime in the 2nd half of 63 will Lincoln be standing again having gone to war over the issue of succession and then being forced to accept defeat and recognise southern independence? I suspect not but if so which way does the party go?
c) Assuming that the north doesn't maintain control of a string of land along the Lower Mississippi and other enclaves it means the south has control of the outlet of trade via New Orleans which is economically very important for a lot of states and territories. This is likely to include some treaty terms that provides the US with uninterrupted access and possibly with no tariffs. However no one in the hinterland is going to forget this means nothing if the two nations go to war again. Which is something many people in those regions will have a vested interest to avoid.
d) Frankly while a lot of blacks who have escaped slavery will want to help their fellows and a number of northerners will want to help them, either for moral reasons or simply because they want to hurt the south. However how many in the north want a lot of freed slaves moving north and competing with them for jobs. This was an important issue both because of racism and because the blacks were often willing to work for lower wages. A prime reason why one of the prime targets of the draft riots were freed blacks in New York. Similarly Lincoln himself had said he didn't accept the idea of racial equality and that black were inferior. This may have been his belief, as it was for most people at the time or simply he needed to take such a stance to get elected. I'm not sure there will be that much sympathy for blacks going south and engaging in acts of violence there, both because it could mean war and because even if they 'won' how many freed blacks are going to want to flee north?
e) Also since the north has explicitly recognised the south's independence by making peace with it any such support would be a clear act of war. As such the government, as opposed to individual elements in the population has to consider the political and international crisis that could develop unless it makes at least some efforts to prevent such actions. A new John Brown will be a hero to the radical abolitionists and the revanchists but would be a real problem for the government.
Any new war would be markedly harder to win as the south is now an internationally recognised state so attempting to undermine it is going to have diplomatic costs, even more so any attempt to blockade it. Furthermore unless the south is totally incompetent - which its possibly they might be - their likely to have defensive forts and river flotillas to make advances through key choke points a lot more costly. Plus a regular army trained and in position. The north is going to have as well but unless its going to maintain a much larger one, which will cost a lot and increase tensions further attacking the south is likely to be costly, in terms of blood, money and possibly political support for such a war.
I'm not saying those problems are insumountable and that a hard line revancist party/bloc can't come to power and decide on violent confrontation with the south but it could go a number of other ways as well.
One other point for you and others. What happens to the northern slave states? Kentucky and Maryland for instance? IIRC slavery is still legal there and Lincoln was careful to protect the rights of slave owners in those states to avoid unrest. It would seem likely that the north is going to move to ban slavely but they might have to be careful here as it could cause unrest in those states, even if suitable compensation is offered. After all by making peace with the south there is an implicit recognition of the right of a state to secede. Its likely there would be some move to change this, I would guess by a constitutional amendment? This would however take some time and could spook one or more states into seceding while they can claim it was legal. True the north could occupy them beforehand to prevent this but that's likely to cause internal and international concern and is a clear excuse for the south, if it chooses to support them in some way even up to a dow although that is likely to be a bad move by them.
Anyway, as you say this is all speculation and so things could go in all sorts of ways. I suspect that even a crushing victory by Lee at Gettysburg is unlikely to end the conflict, although if it did prompt European recognition of the south things could move fairly decisively from there.
Steve