Metarln
It looks like instead of them dying, the MC transfered them via time-hopping into the future. In a sense they still vanish from acting in the timeframe they are supposed to be dead and it would explain why Ryuu still has contact with her Goddess as well as knows Aston. Her not wanting to divulge more information than needed means MC probably told her to keep changes to a minimal degree so that not an unforeseen butterfly effect occures.