a) your arguments are all over the place
"If Hitler unveils himself after the last war/Holocaust victim dies"..."it also is unfair to the victims... they deserve to watch the arrest and conviction"
So are they dead or aren't they?
"who is anyone to pass judgment on him for war crimes"..."if you were moral, you would arrest Hitler and hand him over to a jury of his peers, and let society deal his punishment"
That's what a war crimes trial is: a *trial* that passes judgement on society's behalf.
b) "they deserve to watch the arrest and conviction"
"all accusers are dead and he cannot face any of them"
"if all accusers are dead and no one can point the finger, do we have any rights under our judicial system to prosecute someone"
You seem to think the judicial system is about giving the immediate victims revenge. It's not. The point is to uphold the idea that actions have consequences, and that justice is valuable for it's own sake. In so doing, we hope to prevent the similar crimes from being committed in the future, but the value of justice for it's own sake is what allows it to stand even when convenience would tear it down.
c) "if all accusers are dead and no one can point the finger, do we have any rights under our judicial system to prosecute someone? Would we launch a full scale forensics investigation"
It would have to be a trial with evidence, but I'm pretty sure you could find enough evidence to get a conviction.
d) "you are passing judgment on someone... someone that never even harmed you."
Just FYI, the idea of 'crmes against humanity' means actions that harmed the dignity and worth of the human race generally. While your friend certainly never got put to a concentration camp or saw his family gassed and stuffed in mass graves or crematoria, that doesn't necessarily mean Hitler's action have no effect on him whatsoever.
e) "Families deserve compensation? Is that like black people having reversed segregation rights... dont 'deserve' anything"
There's a difference between "you kicked my great-great-great-great-great-great-great-grandparents out of their country." (a grievance I could hold and don't, because it would be moronic) and "you made my father's life a living hell for years and then he had to go to a foreign country with nothing because you stole everything he and his family had worked for." The latter is just a bit more personal.
f) bit of a side note, but...
"If Hitler unveils himself after the last war/Holocaust victim dies"
iIf Hitler re-appeared today he would be 110 years old, and I know a few holocaust survivors who are still quite healthy, so actually, it's all a moot point, since he'd be dead.