Guerrilla warfare was already off the agenda. Lee had rejected it, and so had Johnston by opening talks with Sherman - already under way when Lincoln was shot.
The only danger of it was if the North had attempted some of the more vindictive things suggested on this thread. Thankfully, they had more sense.
Davis certainly had not given up and whether the talks between Johnston and Sherman would have gone the way they did in the absence of Lincoln's assassination is doubtful. While the Confederacy as an organized body was doomed, an unorganized rabble continuing on was still possible. Lincoln's assassination had the beneficial effect that the bitter-enders of the South sought the obtainable goal of putting the Negro in his place, rather than continuing to seek an unobtainable independence. By and large the attempt to secede had been a conservative revolution in the first place, which is why Lincoln's assassination was so shocking.