Going back to the two Death Stars idea for ROTJ if the incomplete clone of the original Death Star was the lure the completed Death Star could resemble Starkiller Base the weapon could be badly damaged and it could jump to hyperspace just as the second Death Star exploded.
That way it could be repaired by the First Order or the Base seen in the next film could be based on it. It would take a long time because the First Order wouldn’t have the same resources as the Empire.
Maybe using the star as a power source is a work around for the reactor being impossible to fix.