It’s probably safe to assume that the book mentions she’ll return on her 28th birthday. But even so, why would that suggest to Henry that it was HIS job to go get her? If it’s her destiny to return, then wouldn’t he just figure she’d show up of her own accord without him having to do anything like go and find her and drag her there? So why would he go buying himself a bus ticket?
But if a bus ticket with his name on it showed up out of nowhere, THEN he’d know he had a role to play.