There's been plenty of historical examples where taxing the wealthy has worked. Assets can't easily move countries, nations can enforce taxes regardless of a wealthy person's residence, etc etc etc. Even if this tax is hard to design and implement, it's the right thing to do and it's necessary for our future.
Stop doing the work of the billionaires for free. Properly designed wealth taxes will work in Europe, we're smart enough to figure it out - and again - it's necessary.