Forgiveness is about more than facing the consequences. It should be focused on healing between the perpetrator and victim.
There is no way that any sort of punishment can atone for the crimes a Nazi committed. Forgiving the Nazis will give a Holocaust victim the peace of mind to heal from their trauma without holding onto the negative emotions towards the Nazis. By forgiving someone of their wrongdoings, it does not excuse the actions of the perpetrator. Therefore, whether or not a Nazi is convicted of their crimes should have no bearing on if a survivor of the Holocaust should be allowed to forgive.