Williams was one of the stars as the Chiefs claimed the Super Rugby title with a 37-6 victory over the Sharks on Saturday.
He is set to feature for the All Blacks in the inaugural Rugby Championship against Australia this month before moving to Japan and then returning to Rugby League.
But New Zealand head coach Hanson believes the 27-year-old World Cup winner will be back.
"I think he'll come back," said Hansen.
"He's really enjoyed his time playing rugby and he's really enjoyed the Chiefs.
"I'd be confident to say it's not the last time he'll play for the All Blacks either.
"He's a world class player now. If we didn't pick him, we'd be getting six lashes from the headmaster.
"He's done things that are different and sometimes in New Zealand we don't like people that are a little different.
"That's not to say he doesn't care about his country. We know he does and when I spoke to him about the opportunity [to play in the Rugby Championship], he couldn't answer quick enough with a 'yes'."
Williams has received some criticism for his move back to Rugby League, via a lucrative stint in Japan, while pursuing a boxing career, but Hansen feels this is unfair.
"One or two people think he might be chasing money, but he's a professional sportsperson," added Hansen
"You only get a very short term in your playing career to make money. Doctors are doctors from the time they graduate to the time they die.
"It's not his fault that he's pretty good at boxing and people want to watch him do that. It's not his fault that he's good at league."