umbral era events are in sequence:
1)ifrit fight & cutscene
2)gc company quests
3) moogle ?
4)garuda fight & cutscene
5) live events like garlean invasions
6)soon, castrum novos
7)next patch, imperial fight

So chill out. Even if returners don't manage to see all of this in 10 days, they can still see at least half and things like af quests