During his lifetime he paid almost 150 million euros in taxes, so more than most of us will ever pay - so I think he can go wherever he pleases. And yes, even as a completely non-rich person, I think that the French 75% tax is absurd by every possible measure.
The point is is it doesn't matter how he got rich. He is rich and can afford to flee the higher tax bracket. You can argue it's wrong or immoral of him to do so but none of your arguments will induce him to stay and pay the tax. You try to squeeze the class with the most means and mobility and they just slip through your fingers.
