Aswatthama's right words

 Ashwatthama's was angry after the death of Drona.He said these words.

I have now learnt how my sire has been slain by those low wretches after he laid aside his weapons, and how also has a sinful act been perpetrated by Yudhishthira disguised in the grab of virtue! 1 I have now heard of that unrighteous and exceedingly cruel act of Dharma's son. Indeed, to those engaged in battle, either of the two things must happen, viz., victory or defeat. Death in battle is always to be applauded. That death, in battle, of a person engaged in fight, which takes place under circumstances of righteousness, is not deserving of grief, as has been observed by the sages. Without doubt, my sire has gone to the region of heroes. He having met with such a death, I should not grieve for him. The humiliation, however, of a seizure of his locks, that he sustained in the very sight of all the troops, while he was righteously engaged in battle, is tearing the very core of my heart. Myself alive, my sire's locks were seized, why should sonless people then entertain a desire of offspring? 2 People perpetrate unrighteous acts or humiliate others, moved by lust or wrath or folly or hatred or levity. The cruel and wicked-souled son of Prishata hath perpetrated this exceedingly sinful act in total disregard of me Dhrishtadyumna, therefore, shall surely suffer the dreadful consequence of that act, as also the false-speeched son of Pandu, that has acted so wrongly. Today, the earth shall certainly drink the blood of that king Yudhishthira the just, who caused the preceptor, by an act of deceit to lay aside his weapons. I swear by truth, O Kauraveya, as also by my religious acts, that I shall never bear the burden of life if I fail to exterminate the Panchalas. By every means I contend with the Panchalas in dreadful strife. I shall certainly slay in battle Dhrishtadyumna, that perpetrator of unrighteous deeds. Mild or violent, let the means be what they will, I shall effect the destruction of all the Panchalas before peace becomes mine. O Kaurava!

So Ashwatthama killed drishtyadyumna ,and other brothers of draupadi on thenight of Duryodhana's death.He also killed Draupadi's five sons.He didnt want panchala descendents to live.Saputika parva was part of shalya parva.It was later made into a separate parva by later editors of Mahabharata.Its not a play or added later.The Hindu rightwingers want to believe that sauptika parva is added later becasue it negates the victory of the pandavas.And the pandava victory will be useless.Thethe truth is pandava victory is not useful.That is what makes mahabharata an epic.Mahabharata is not a happy ending story.It is these things that made mahabharata popular for  along time.
Ashwatthama was caught by pandavas as he agreed that he didnt know how to withdraw the Brahmashira astra.And Arjuna with this permission has withdrawn both the astras.Draupadi has to let Ashwatthamam go.Because by now she realised that revenge is not good.It took this much time for her to realise this.
And krishan curse to Ashwatthama is false.Ashwatthama certianly didn't live thousands of years.That is made up by some.He went away somewhere after this.