I say forget the old story line, say eir got revived and after a couple of years, all the heroes of Lunia (aka sieg, dainn, eir, etc) get frozen so they dont get older and stuff.
Centuries later, they find themselves revived in a totally new world, but with the same old problems. What do they do next?
OR you can say that sieg/dainn/eir/tia lived a happy life. Sieg married tia and gave birth to asuka but since she was a cross between an elf and a human, she can live for a very very long time (lols). Dainn married eir cuz he fell in love and they just chilled, had a kid.. w/e w/e...
Centuries later, the world finds itself in trouble again, but instead of having a story with the same old sieg/dainn/eir/tia, the story would be with Ryan, arien, asuka, and w/e other secret chars you can think of... HOW ABOUT THAT!
Theme of episode 7 can be...... im not sure... has to be futuristic, maybe in the days of space and time travel.
Edit: YEA TIME TRAVEL, they can go back in time so they can get guidance from the old heroes of the world, meaning sieg/eir/dainn/tia and asuka can see her parents again.... and then they go bak to defeat the evil do-er of the present day..... lol