After dragging Fred's body to safety, Harry, Ron, and Hermione somehow force themselves - and each other - to continue going after Nagini.

Harry dives inside Voldemort's mind, trying to discern his location - and discovers him to be in the Shrieking Shack, sending Lucius Malfoy to find Snape.
Trying to decide how best to go after Nagini, the trio is ambushed by Death Eaters and spared by some quick spellwork from Hermione. They then throw on the [Invisibility Cloak] and run through the battle, watching small victories for both sides, including Hagrid as he is carried off by [acromantulas]. They are saved from [dementors] by Luna, [Ernie], and [Seamus], and finally make it to the [Whomping Willow] and inside.
Harry leads Ron and Hermione down the tunnel to the Shrieking Shack where, hidden under the [Invisibility Cloak], they watch Voldemort kill Severus Snape in order to gain mastery of the [Elder Wand]. He departs with Nagini and Harry rushes to Snape, who urges Harry to take the memories gushing from his mouth, ears, and eyes, and then dies.
Still sitting in the Shrieking Shack, Harry hears Voldemort's voice commanding his army to pull away, and demanding that Harry meet him in the [Forbidden Forest] within the hour.
Harry, Ron, and Hermione make their way back to the castle, with scenes of destruction meeting their eyes: the Weasley family mourning Fred; Lupin and Tonks lying together, dead; and a castle ripped to shreds.
Reeling from the [Great Hall], Harry runs to [Dumbledore]'s office, pours Snape's memories into the [Pensieve], and dives in.
Snape's first memory: Snape watches as Lily and [Petunia Evans] play on the playground, Lily jumping far higher off the swing than any Muggle could. When Snape jumps out to tell Lily she's a witch, though, the girls laugh and run off.
Snape's second memory: Snape and Lily sit, talking about [Hogwarts], and Snape tells her about the school and about [dementors]. When Snape catches [Petunia] spying, though, he drops a branch on her head and she and Lily run off again, irate.
Snape's third memory: On [Platform 9 3/4], Lily prepares to leave for school with an angry and jealous [Petunia] saying goodbye. Lily lets slip that she and Snape found the letter [Dumbledore] wrote back to Petunia, though, leaving her angry again as she runs away from her sister.