Flynn (or maybe Porter) may have been an emergency callup but he's not anymore. Emergency callups are when you aren't able to field a full team. 12 F 6D and 2 goalies. Sabres have been able to do that and Flynn/Porter was still here. So it's no longer an emergency if it was to begin with.
Flynn and Porter don't have to clear waivers, they don't have enough games yet. They could send Grigs back to juniors. FWIW the next game would be number 23 for him.