I understand that it is currently not supported from the Author - Stefan Kohlbrecher https://answers.ros.org/question/47496/hector_slam-how-to-load-a-saved-map-and-perform-localization/

But I also understand that @Jin-W-FS had made a PR on Load Static Map #45 https://github.com/tu-darmstadt-ros-pkg/hector_slam/pull/45