> Some companies might leave but they are not better off elsewhere in the EU so I think most will stay.

Probably not, if they haven't already; this relates to Apple's tax structure between 1980 and 2014 (ie not currently), and the key issue is that Apple was given unlawful state aid; Apple was advantaged over other companies, and Ireland was advantaged over other member states, which the EU restricts (interestingly, AIUI this would likely have been legal in the US, where states are generally allowed give special tax benefits to specific companies).