Bungie haven't said yet, but because seraph shield is being vaulted for a few seasons there is a very good chance that the catalyst quests wont be available - but if they are available when lightfall launches it will be done through a completely different way than seraph shield. They may just add them to the playlists like they did for other exotics but they may decide to hold them back until seraph shield is readded in season 22. If you have the time - you should get them done before Monday daily reset