Should I leave the existing ventilation fans in when getting a new metal roof installed?

I am replacing my shingle roof with a metal one. The contractor that is going to install the roof recommended that I remove the existing ventilation fans. The attic gets really hot. But the contractor told told me the metal roof will act as a good insulator and the attic fans aren't needed. Can I get someone's professional opinion on this. I know it would be easier for him to install the roof without the fans. But I'm not sold on the idea that the roof will insulate well enough to eliminate the need for a fan.