In the context of the recent ECJ decision in W AG (Case C-538/20), this article examines whether the ECJ has possibly, de facto, abandoned the legal concept of final losses or whether it wants to see it continue to be applied as a restrictive ultima ratio exception (based on its long line of case law) in accordance with the principle of proportionality. In this respect, the ECJ’s line of case law will be analysed, including the recent decision in W AG on final losses from permanent establishments exempt under a tax treaty.