Voldemort would have successfully killed Neville that first night. The only reason Harry survived was because his mother was given a choice to live (because Snape had asked Voldemort not to kill her) and chose to die for her son. Voldemort would have had no reason to give either of Neville's parents a choice - he would have just killed them, then killed Neville.

It's also why James' death didn't save Lily - he wasn't given the choice, Voldemort had always intended to kill him.