Spoiler Alert!!!
Not a very realistic ending. RJH would be lucky to go from North Korea to Switzerland not every year but probably once every 10 years, the way orchestras tour. Also, the Swiss gentleman who spoke with Seri said that there were North Koreans in the program THAT YEAR, implying it was unusual, and not the norm. So RJH could not just waltz off to Switzerland for two weeks every year. And that's not even getting into the fact that he hadn't touched a piano in 7 years. There would be dozens of North Korean pianists ahead of him in line.
A much more realistic ending would have been if RJH had been posted to the North Korean embassy in Bejing as an attache. RJH's father as #3 man in NK could easily make that happen. Seri could run her business from Bejing, shuttling back and forth to Seoul. It wouldn't be a perfect solution, but a lot more realistic than this Swiss pipe dream, and it wouldn't mean just two weeks a year, which they portrayed in CLOY as all flowers and smiles, but in reality would be a kind of torture for both of them.
I think the two weeks in Switzerland ending might have been dictated by the expense of shooting there, which is very unfortunate, IMO. They had to justify going all the way over for filming. Certainly, portions of the final scenes in Switzerland don't make any sense, with the lack of rings chief among them. It was one of the most moving moments in the entire drama when Seri said she would "never take off her ring." But it wasn't there in the final scenes.
I will always cherish episodes four through nine, which to me were the heart of the series. Once Seri got back to Seoul, all the fun and charisma of her character got washed away. RJH's character was also much less interesting in Seoul. Aside from the drunken confession scene, the ring exchange scene (which really needed a kiss or a hug at the end) and the border scene in ep. 16 (so powerful!), the Seri-RJH story stagnated after she crossed the border in ep. 9. The ending certainly didn't help in that regard.
I'm sad, because I loved this drama to about the halfway point, but afterwards I though it got fairly predictable and melodramatic. And the ending didn't work for me at all. They are supposed to be happy when they are apart 95% of the time, with no chance to have a family? They would not be happy in real life.