how long you think the time gap will be from the end of the 7th umbra and our characters coming back?
short: 1~4year the new big trees can be explained that dalmund had super fertilizer or something.
mid 5~10 years i think this one is more likely since NPCs wont get much older and it gives time for changes
long : 11~50 years , dont think so since we know the emperor is the main antagonist and don't think he got that long to live :P