Correct. Michigan only requires 50%+1 for a quorum, so a minority cannot shut things down by walking out.
One other note -- there are two bills that have to be passed. The one that passed earlier related to public sector unions. The one being discussed now relates to private sector unions.
They're just starting to vote on the second bill (go to house.michigan.gov and you can watch).
The second bill was adopted. There was a parliamentary maneuver by the GOP to reconsider the vote, which means it will not go to the Governor until tomorrow, but the bill has been adopted in the same form as the Senate, so it will go to the Governor tomorrow.
MI House passed both Public and Private Union Freedom to Work in Michigan. 58-51 58-52