The EU is not punishing the UK for leaving - the UK is leaving and for the future is trying to arrange an outsider's agreement beyond the norm (WTO etc.). The UK would gain if it gets what it wants, the EU would gain if the conditions are right. The two are talking (sometimes) and maybe an agreement will result but, one would assume, only if it suits both or at least both accept it - that has not been the case while the UK has been a member (repeated UK moans) so maybe the EU has learned not to bother making agreements with the UK ("changed our minds, don't like it anymore, Wah, kick, scream, insist on a concession"). There is no reason to think that the EU would punish any member, whether old, new, or returning.