The silver hand Lord Voldemort had given Pettigrew interpreted his hesitation as weakness and/or disloyalty, and strangled him to death, saving Harry and finally finding redemption for his treason, despite his reputation remained tarnished as many remained dubious of the evidence of his innate bravery.

How did wormtail save Harry?

Unfortunately for Voldemort, his attempt on Harry's life backfired and he was practically disintegrated. Wormtail deduced this once he came across the rubble of the house. He then found Voldemort's iconic phoenix-feathered wand and took it for safe keeping.

How did Peter Pettigrew repay Harry?

This was repaid when Pettigrew hesitated and showed a fleeting moment of mercy at the Skirmish at Malfoy Manor and released Harry from a choking hold with his silver hand, which Voldemort had given to him for sacrificing his own hand to bring Voldemort back into human form.