However, IOTL the north could retire having achieved most of its objectives: union preserved, southern primacy on national political power broken, chattel slavery abolished. Here they would be walking away with none of those, and considering that guerrilla movements rarely succeed except with powerful foreign backing, I don't think the odds are in the south's favor militarily either.
Depends what you mean by "succeed".
When the Boers resorted to guerilla warfare, it did not succeed in preserving their independence, and indeed exposed them to extremely harsh British counter-measures. However, it did make Britain eager to get the war finished, and secured the Boers very moderate terms of surrender, crucially including a promise that any decision on giving black Africans the vote would not be raised until Transvaal and OFS had been granted self-government and could decide this for themselves. I could imagine a guerilla war in the South ending the same way.