The end of the UN seems plausible if we continue to move from a rule-based world order to a power-based one. For the same reason, there is little chance we will see the end of the EU. No European country is sufficiently powerful to really matter on the world stage, a more united Europe has the potential to be a significant world power though.
Thank you! Every single time when people will start about EU falling apart, alternative is what? Being a Russian colony? Whatever harebrained things EU can come up with is lightyears better than than Russian ideas or being just a rug for China.