I'm sure Peter will help in the end. It's all set up.

"Pettigrew owes his life to you. You have sent Voldemort a deputy who is in your debt... "
"I'm much mistaken if Voldemort wants his servant in the debt of Harry Potter... "
"This is magic at its deepest, its most impenetrable, Harry. But trust me... the time may come when you will be very glad you saved Pettigrew's life."