I would have been stunned if he didn't win the momentum behind him was massive, Reform hasn't gone away smaller parties including the Tories came nowhere.
There is every reason why MPs rally round Burnham and depose Starmer immediately, they obviously want a change so why wait until after the summer break. Burnham "talks the talk" and should unite the Labour Party whether he can score enough successes to win the next election will be the real test.