How did Dhritarashtra die in the Mahabharata? I couldn't get the answer in Wikipedia unfortunately.
The death of Dhritarashtra is described in this chapter of the Ashramavasika Parva of the Mahabharata. Fifteen years after the Mahabharata war, Dhritarashtra, Gandhari, Kunti, Vidura, and Sanjaya all went to the ashram (hermitage) of the sage Vyasa in order to become Sanyasis, in order to escape the sorrows they had suffered. Vidura died first in the ashram. After that, the rest of them decided to go to Gangadwara (modern day Haridwar) and engage in Tapasya on the banks of Ganga river. one day there was a forest fire, and Dhritarashtra, Gandhari, and Kunti all allowed themselves to be consumed because fire is a fitting death for Sanyasis.
One day, that best of kings proceeded to a spot on the margin of Ganga. He then bathed in the sacred stream and finishing his ablutions turned his face towards his retreat. The wind rose high. A fierce forest-conflagration set in. It began to burn that forest all around. When the herds of animals were being burnt all around, as also the snakes that inhabited that region, herds of wild boars began to take themselves to the nearest marshes and waters. When that forest was thus afflicted on all sides and such distress came upon all the living creatures residing there, the king, who had taken no food, was incapable of moving or exerting himself at all. Thy two mothers also, exceedingly emaciated, were unable to move. The king, seeing the conflagration approach him from all sides, addressed the Suta Sanjaya, that foremost of skilful charioteers, saying,--'Go, O Sanjaya, to such a place where the fire may not burn thee. As regards ourselves, we shall suffer our bodies to be destroyed by this fire and attain to the highest goal.' Unto him, Sanjaya, that foremost of speakers, said,--'O king, this death, brought on by a fire that is not sacred, will prove calamitous to thee. I do not, however, see any means by which thou canst escape from this conflagration. That which should next be done should be indicated by thee.'
Thus addressed by Sanjaya the king once more said,--'This death cannot be calamitous to us, for we have left our home of our own accord. Water, fire, wind, and abstention from food, (as means of death), are laudable for ascetics. Do thou, therefore, leave us, O Sanjaya, without any delay. Having said these words to Sanjaya, the king concentrated his mind. Facing the east, he sat down, with Gandhari and Kunti. Beholding him in that attitude, Sanjaya walked round him. Endued with intelligence, Sanjaya said,--'Do thou concentrate thy soul, O puissant one.' The son of a Rishi, and himself possessed of great wisdom, the king acted as he was told. Restraining all the senses, he remained like a post of wood. The highly blessed Gandhari, and thy mother Pritha too, remained in the same attitude. Then thy royal sire was overtaken by the forest-conflagration. Sanjaya, his minister, succeeded in escaping from that conflagration:
So only Dhritarashtra's minister and charioteer Sanjaya survived.