I don't think I made myself clear, which is lwk my fault, what I meant is that you can get it back by replaying his route, he will replace nulla's with his, does he comment on it? no, he just replaces it and that's pretty much it.
Are you perchance skipping through the dialogue or changed a bit some of your choices? Because I think that may be the issue on why, try to do the same choices you did when you first got his icon, also I did their routes again just to make sure so i went to septem's to nulla's to doing septem's once again and yes he replaces the icon.