There is one problem. They can´t do it another time. The Hourai are still truly immortal. But since the SDM crew won´t go to mars again the cyrcle will repeat with them landing on Shiva again but Eirin will never encounter Sakuya in space since they didn´t try to go to mars. That means this time They can´t force activate a new Big Bang. That means yeah the reconstructed their universe one time but won´t be able to do so another time. that means the second time they truly will fly in space until the end of time.
Still a really great story. And I never thought I would find Sakuya with such a big role. She is my favorite after all. Sadly no Meiling though.