SeaGtGruff wrote: »After your ESO Plus paid subscription or free trial ends, you will no longer be able to travel to the zone and quest there. Any skyshards and skill points you've collected, achievements you've earned, etc., will still be yours to keep even though you can no longer travel to the zone and quest there. But (as far as I know) you should be able to buy the skyshards on your other characters if you wish. Also, the progress you've made on questing and discovering things (including wayshrines) on the map will still be there, such that if you ever purchase the DLC, or subscribe to ESO Plus, or make use of another ESO Plus free trial, you'll be able to go back to the zone and continue where you left off.
I'm not sure about the Dark Brotherhood. I think you should retain the skill line and any progress you've made in it, including the Blade of Woe if you've unlocked that, but since you won't be able to travel to the zone and quest there it won't be possible to continue doing daily and repeatable quests there. But I'm not sure whether you'll still be able to level up the skill line (not the individual skills you've already unlocked, but the skill line as a whole).