Erwin Rommel, The Desert Fox, is a popular and enigmatic figure in military history. Having been forced to commit suicide by the Nazis -- he was given the alternative of suicide, or a public trial for treason, with the consequent destitution of his entire family -- has become something of a martyr and legend for people on all sides of WWII. He almost certainly knew about, and approved the Von Stauffenberg bombing plot to kill Hitler, in 1944, but, he wasn't involved in the planning to any extent. This was enough for Hitler to want him dead, so, the Nazis arranged it.
Rommel was somewhat unique, in that he was respected by all sides, even at the height of the conflict, as an honorable and brilliant commander and general. He had no significant involvement in slave labor programs, extermination campaigns, the murder of civilians, or any other activities normally associated with war crimes. He was a brilliant and successful Nazi general, who was frequently used by Hitler for popular political purposes and propaganda, because of his effectiveness, his charisma, and his courage.
So, let's just suppose that Rommel survived the war. Perhaps Hitler decides he needs Rommel too much to kill him. After all, Albert Speer is supposed to have known about the plot, and the plotters were even planning on keeping him in his position of Minister of Armaments and Munitions, if their plot had succeeded! Nevertheless, Hitler never touched Speer. He probably found him too useful. Perhaps, he might have changed his mind, and decided to spare Rommel as well, for the same reason. Or, quite possibly, if Rommel had refused the option of suicide, Hitler might have decided a public trial and humiliation of such a popular figure simply wasn't worth the political fallout, and might have backed off, at the end. Hitler was always very, very sensitive to German popular opinion, which is why he had such a hold over the German people.
So, once they win the war, what exactly do the allies decide to do with Rommel? Will he be charged as a war criminal? On what basis, exactly? After all, Werner Von Braun and his merry band of engineer-rocketeers was certainly involved much more in killing civilians, slave labor programs, and war crimes in general, but, they were never touched at all! Von Braun wasn't merely a member of the Nazi Party, but a member of the infamous SS, responsible for the Jewish Holocaust. Why go after poor old Erwin Rommel? Rommel was never even a member of the Nazi Party, and openly disapproved of their policies!
It might be instructive to compare the case of Admiral Donitz, the head of the German navy, and, hence of their highly successful U-boat campaign. Donitz would have employed slave labor in building his ships, and, his U-boats targeted civilian and military alike. Furthermore, his U-boat blockade of Britain was highly successful, and put the entire nation at risk of starvation. Yet, despite all this, he only got a ten year sentence at the Nuremberg war crimes trials.
So, why would Rommel have been charged as a war criminal, at all? For what purpose? The Soviet Union, and Josef Stalin, who had suffered the most from the war, probably wouldn't have given a damn about Rommel one way or another. They never even fought him, he wasn't a Nazi, he was just a terrific general, and the Russians respect great generals, even amongst their enemies. I suspect even the Russians wouldn't have insisted on Rommel being charged for war crimes.
So, I strongly suspect Rommel wouldn't have been charged with anything at all. He would simply have been an old, highly respected general, respected by friend and foe alike, and, would likely have gone into German politics, with some success. As his son eventually did, of course, OTL.
Erwin Rommel represents something fairly unique, the "good general", the noble warrior. He reminds me a bit of WWI German air ace Baron Von Richthofen, who was shot down over enemy lines after having shot down 80 allied airmen in the course of the war. The allies buried him with high honors, and some even cried at his funeral!