When did the situation facing the South come to that point when surrender and the salvage of as much of it's national treasure, private property and blood of it's youth outweighed any hopes of defeating the North?
Some things from my perspective.
1) Lee carried the hopes for the South. He performed some good work in the East with some good tactical victories which kept the Confederacy alive. The Confederates' hopes, dreams, confidence hinged on what he did and eyes were on him.
2) The Western Theatre was a disaster from the get-go for the Confederates. I believe that Lee in the East at least mitigated these setbacks in terms of emotional/physical loss therefore giving the Confederacy SOMETHING to cling to......if things were going on in the East, then all the losses the Confederacy sustained elsewhere would still be worth it.
3) If Lee could keep things going in the East, then every loss of treasure , youth and infrastructure would be worth it for independence.
4) When he tried to link up with Johnston after slipping out from Petersburg by heading West, there was still hope.
5) He just couldn't overcome the Union as he was moving West. Lee I believe at this point he saw what was happening and what was going to happen......it was THIS point where surrender became more important than defeating the North.
6) It doesn't really matter when historians think at what point it was or when other commanders in the war thought at what point it was. If Lee was still active in the field, directing the movements etc.....then that point would come later, regardless of what failures were happening elsewhere.
My response is very Lee-centric, I am aware of this. I believe that what he did and thought decided (in the minds of Confederates) what was worth it and what wasn't worth it.
So one could say that it took the whole war to get to the point where surrender became more important than defeating the North.