I myself was not sure whether it was Indra Dev's revenge - just a doubt I had.
But Lord Krishna's death was caused by a hunter if I remember correctly. And there was a story behind that . . .
After the war, when Gandhari was weeping in the battle field she blamed Lord Krishna for all the destruction caused. She said that if He had intended to, He could have stopped the war and saved everyone from destruction.
Krishna smiled and said that he was standing in front of her. Gandhari became so angry and cursed him that in exactly 36 years his own family will die quarrelling among themselves and that the sea will swallow the city of Dwaraka and he will roam around with no one to care for and die alone.
Krishna said that he already knew that these will happen and as the Yadavas could not be killed by humans, demons, gods or anyother creatures, they have to kill themselves to become extinct. He also advised her to join the funeral rites so that the dead souls may attain peace.
Another story -
Krishna prayed to Lord Shiva for a son like him (Shiva). This wish was immediately granted. When Parvati enquired as to why LordKrishna wanted a son like him, Lord Shiva replied that as he was the Lord of destruction Lord Krishna wanted a son who would bring destruction.
This son named Samba was a real nuisance for his father Krishna. Krishna was ashamed of him for many reasons. It was said that he had abducted Duryodhan's daughter without her consent from the Swyamvara hall.
He was too playful and sarcastic. One day, he and his friends, planned to tease some sages living near their palace. Samba diguised himself as a pregnant woman and he and his friends asked the sages whether the baby to be bron will be a boy or a girl. The sages, outraged at their insolence, cursed them saying that this person (Samba) will bear a mace that will destroy your whole race.
To their absolute horror, Samba and his friends discoverd the mace in his clothes. They ran to Akrur for help and he suggested that they grind the mace and throw the powder into the sea. They did as he advised but one triangular piece of iron could not be ground at all. They threw it as such into the sea. This piece of iron was swallowed by a fish and later on the fish was caught by a hunter. Upon discovering the piece of iron in the fish, he used it for an arrow head. This was the same hunter who killed Lord Krishna.
The powdered mace was washed ashore by the sea and a particular type of grass grew from it. After some years, the Yadhavas started quarrelling amon themselves and these quarrels became fights and wars. All their weapons have been destroyed in war and so they pulled the grass that had grown on the shores and threw it at eadh other. This grass turned into terrible weapons and in the battles that ensued everyone of the Yadhavas were killed except Balram and Krishna. Balram was sick of the world and he gave up his life through meditation. Krishna was killed as he was resting in the forest. The hunter thought that he was a peacock resting under a tree.
When the sea had claimed the lands of Dwaraka, Arjun took Anirudhra (Krishna's grandson) and those who were left to Hastinapur. After that, no one knows what happened to the Yadhavas.
This is all I know. I don't know where the incarnaions of Vaali or Angad came in. Vaali as far as I can recall reached the Lord's feet and was not born again. As for Angad, he was devoted to Lakshman and Lord Ram. I cannot imagine him being reborn to kill Krishna.
