Is Doraemon ended?
So actually, Doraemon has NEVER OFFICIALLY ENDED. All endings are fictitious and written by fans which has been circulated and made into videos. The original creators have never issued an ending. They did come up with an ending with Doraemon returning to the future but they scraped it and continued the series.
Does Doraemon leave Nobita?
In 1986 a end was proposed by the author in which Doraemon ,in which he leaves Nobita and goes back to the future. But later they decided to continue the manga. You can consider that the ending proposed was exactly same as the ending of movie Doraemon stand by me , except Doraemon returning from the future.