After Mahabharata, there is no major presence mark made by Pandava and Krishna. What happened to them after that?
After Mahabharat they return to their respective kingdoms, rule for few decades (around 35 years) and then leave this world for ever having served their purpose of life. The Mausala Parva and the Mahaprasthanika Parva of Mahabharat has the detailed description about it. The major events in breif are:
Thus, after many such series of events Shri Krishna and the Pandavas leave this mortal world. The city of Dwaraka submerges into the ocean and eventually the present age of Kali begins.
Reasons for which the Pandavas fell down from the mountain
As per Ankit's suggestion (with reference to the point 8 above) below are the reasons, as given by Yudhisthira to Bhima, for which the Pandava brothers and Draupadi except Yudhisthira fell down from the mountain:
If you ask me , what happened them after they left their body, here is the answer.
Bhisma attained to the status of the Vasus.
Drona entered into Brihaspati
Kritavarma entered the Maruts.
Pradyumna entered Sanatkumara
Dhritarashtra and Gandhari obtained the regions,that belong to the Lord of treasures
Pandu proceeded to the abode of the great Indra
Virata and Drupada, the king Dhrishtaketu, as also Nishatha, Akrura, Samva, Bhanukampa, and Viduratha, and Bhurishrava and Sala and king Bhuri, and Kansa, and Ugrasena, and Vasudeva, and Uttara, that foremost of men, with his brother Sankha entered into deities
Abhimanyu entered soma
Karna entered Surya
Shakuni obtained absorption into Dwapara
Dhrishtadyumna into the deity of fire
The sons of Dhritarashtra were all Rakshasas of fierce might obtained heaven.
Both Kshattri and king Yudhishthira entered into the god of Righteousness(Yama?)
16,000 women had been married to Vasudeva transformed into apsaras Ghatotkaca and others, who were slain in the great battle, attained to the status, some of gods and some of Yakshas