there are 2 other different endings, those are less optimistic(or even hateful).
one of them is that all that happened in the manga is actually nobita's delusions. he actually suffers from autism.
the last one is that nobita fell and hit his head on a rock. he fell into a deep coma, and eventually into a semi-vegetative state. to raise money for an operation to save nobita, doraemon sold all the tools and devices in his four-dimensional pocket. however, the operation failed. doraemon sold all his tools except for one used as a last resort. he used it to enable nobita to go wherever he wanted, whichever time era he wished to go. In the end, the very place nobita wanted to go was heaven.