Oh no, we are very much stuck here and all manners of attempts to break the barrier have failed. Many, if not most have made attempts. I have made a number myself. Higher-level magics fail entirely and everything else is like shooting sparks into the void. To assume that people have not been studying, experimenting, and making daily attempts is your mistake.
Did I not answer your question to satisfaction? Yes, individuals have left and then returned. It's quite normal, really. And yes, circumstances in their worlds have carried on as if they had been there the entire time. Some remember their time here while others do not.