Here's an interesting question: under these guidelines, was Lee wrong to surrender at Appomattox?
I think under these guidelines, it was still permissible to surrender. Of course, we don't have a large scale surrender of U.S. Army forces since the surrender of the bulk of the 106th Infantry Division in the Ardennes in 1945, but Bataan, Corregidor and the unfortunate 106th Division make for good examples.
In Bataan, the Orion Bagac Line had been cracked, the troops unable to mount vigorous counterattacks after months of rationing and General Edward P. King explicitly stated, "I feel that further resistance would only uselessly waste life."
At Corregidor, U.S. troops were unable to destroy the Japanese beachhead and the landing of Japanese tanks, which they were unable to engage effectively, prompted the surrender.
At the Ardennes, 2 of 3 regiments of the 106th Infantry Division were encircled. They initially held out a perimeter defense, but low on food and ammunition, they attempted to breakout to St. Vith. Failing to do so, they had to surrender.
In the case of Appomattox, Lee has lost a lot of men at Sailor's Creek, his subordinates have urged surrender and his men had little to eat. At Appomattox Court House, the Confederate position was hopeless.
Humphreys's Il Corps and Wright's VI Corps were positioned to attack the Confederate rear at New Hope Church. The way south was blocked by Ord's Army of the James, Griffin's V Corps and Sheridan's cavalry. A breakout attempt was made by Gordon's Corps, briefly pushing Federal cavalry back, but backed down when faced by Ord's infantry. The only avenue of escape left open to Lee was to the northwest, which was devoid of major highways and blocked by a bridgeless James River.
With no avenue of real escape, a failed breakout attempt and an enemy ready to go in for the kill, Lee had done his best for the Confederacy, and he owed it to his men not to be senselessly killed in a futile battle.