Well I think that they had it planned out pretty well. If Jacob and Nessie ran to Rio then Alice and Jasper could *somehow* find them. They would have to keep searching South America for the legends, BUT Alice probably knew that they would find Nahuel. I think things would've worked out and Bella and the rest of the Cullens/Denalis/other covens etc. would have fought off most of the Volturi. DEFINITELY Demetri. They wouldn't have died for nothing, they would have made SURE that he was killed so Jacob, Nessie, Alice and Jasper could go on without them. I think Alice and Jasper would have raised Nessie and eventually, she would have married Jacob when she was of age.