Straw Hats aren't going to backtrack straight back to Red Line at this point of story, it would make no sense. It's more likely that Sabo was framed for the assasination attempt at Vivi and like Deicide said Vivi was also branded a criminal since they failed to kill her. This would be great as it would allow Vivi to meet rest of Straw Hats again soon and get to know them personally, even if she wouldn't continue to travel with them to Laugh Tale. Her strength really isn't an issue storyvise as there is always a possibility that Monet's fruit already on the ship. How interesting it would be that a desert kingdom heir would eat Snow Logia?
If there will ever be a Marineford 2.0, it the finale and the one being on execution stand will be Luffy, not Sabo. It would give a nice excuse for the whole Grand-Line to go fight for him or see him get killed.