Please vote for, and comment on these two trackers, which request the ability to save a partially completed rubric and come back to complete it later:
https://tracker.moodle.org/browse/MDL-52323
https://tracker.moodle.org/browse/MDL-74617
https://tracker.moodle.org/browse/MDL-52323
https://tracker.moodle.org/browse/MDL-74617