What higher honour for me than to talk to a Fairy?

This question you asked deserves a long answer, 'coz you really need to understand the events preceding Shri Krishna's departure, for you to properly appreciate the significance of his "departure" & why his departure is so different from Shri Ram's.

When Shri Krishna established a huge city Dwarka & became Dwarkadheesh (Emperor of Dwarka), people under his protection became all powerful & ruled the Earth. Then Shri Krishna made sure (by helping Pandavas throughout) that morally corrupt & debauched Kauravas of Hastinapur (near today's Delhi) got their just deserts for their evil deeds like trying to disrobe queen Drupadi in front of everybody in the court. But after kauravas were gone & under the twin rulers of Shri Krishna in Dwarka & Yudhisthir in Indraprasth (very near today's Delhi) the people in Shri Krishna's kingdom were so powerful, that Lord realized that if I am to go leaving any of them behind, they may end up as bigger threats to dharma & dharmic ways of life than even Kauravas. So I'll make sure that all of them are gone before my departure.

Compare this with Shri Ram's reign as Ayodhyadheesh. During his reign, people living on this Earth has been described as, "All were unaffectedly good, pious & virtuous; all were learned & accomplished—both men & women. Everyone recognized the merits of others & was learned & wise; everyone recognized the services & benefits received from others. Every husband was pledged to a vow of monogamy & every wife devoted to her husband.

Shri Ram, emperor of Ayodhya, was the undisputed sovereign of the entire globe girdled by the seven oceans. However, to those who realize the infinite greatness of the Lord, even this description of Him as the sovereign of the entire globe, sound highly disparaging."

Now I know that Shri Ram & Krishna being the same person, comparing any aspect of his various divine manifestations is beyond my abilities, yet Fairy, from the last two posts, try to figure out the basic difference between people of the Earth living under Shri Ram's & Shri Krishna's reign, & that will help you understand why the departure of Shri Ram & Shri Krishna is so different.

That's why I've heard a few old people in India saying that regardless of the odds against us in today's world, we should strive to bring back at least some attributes of "Ram Rajya" today, if we really wish to see a peaceful world around us. 

Now to answer your question.

Realizing that people in his kingdom have become power-drunk thanks to unimaginable prosperity, Shri Krishna decided to send them packing before leaving himself. Many sages were staying in a place called Pindarak near Dwarka. One day, some young boys of Dwarka dressed the son of Shri Krishna & Jambavati (daughter of Jambavant, the bear king you're watching these days in Ramayan. How come his daughter got married to Shri Krishna? I'll tell you that story in a day or two) named Samb, as a pregnant young lady & went to the sages & asked them to tell whether this pregnant young lady will give birth to a boy or a girl. The rishis were very angry seeing that supposedly cultured boys from well-to-do families, which included a son of Shri Krishna, were indulging in such ridiculous pranks. They gave them a curse that a big iron rod will appear out of this boy's stomach who is dressed as a pregnant woman, & that rod will destroy your clan. Immediately, an iron rod appeared out of Samb's stomach. Terrified, the boys went running to Dwarka & told people there about this curse. They decided to crush that iron rod into tiny pieces & throw those pieces in the ocean, & did likewise.

Unknown to everyone, those pieces came back to the sea-shore near Dwarka, in an area called Prabhas, & there they grow in the form of Eraka grass. One tiny piece of that iron rod came in possession of a hunter named Jara, who fused that piece on the tip of an arrow which he used for hunting wild animals.

36 years after the Maha Bharat war, Shri Krishna decided to "leave." He asked all the old people, women & children of Dwarka to go to a place called Shankhodhar & wait for Arjun there who will soon arrive to take them to Indraprasth. He asked all young men to came with him to Prabhas to do some Vedic rituals & worship etc. However, once this party reached Prabhas, young men of Dwarka, instead of worshipping etc. started drinking liquor, & they kept drinking as if there is no tomorrow. (Again, this should give you a fair idea, Fairy, why Shri Krishna decided to send these away before leaving.) Shri Krishna kept watching this but did nothing. Once everyone was duly drunk, they started without amongst themselves. Soon, it became a brutal fight, with everyone trying to kill everyone. So drunk were they, so out of their mind, they started taking out Eraka grass from the ground near sea-shore. However, as soon as some Eraka grass came out in someone's hand, it turned in to a huge iron rod. Soon, everyone was killing each other with those rods, & that's how they all died.