I've always been a Europeanist and since I believe we are headed back to a Great Power Politics of the pre-WWI world, I'd like to see Europe standing united in the 3 or 4 great power competition that the 21st century is shaping up to be.
But I don't think you'll see the loss of the US as a global player anytime soon. Not in our lifetimes. You're more likely to see China go down that path as its growth is unsustainable and its demographic future is downright bleak as it grows old before it grows rich.