We can see at least three different scenarios.
First. The win of the Independents can start a democratic process for the independence of Catalonia. This could create a domino effect in other Countries, like in Scotland or Belgium. The tensions could increase and new referendum could take place in those countries.
Second. Madrid imposes its power and no changes will be done in the relation with Catalonia. This could create a very fluid and nervous situation. The unilateral declaration of independence of Barcelona could be an unexpected outcome. And after that, the unpredictable reaction of the Central Government.
Third, the most probable, the new strong power of the Independentists could reasonably bring to a new Constitution with a real federalism. This option could preserve the unity of the State giving, at the same time, an answer to the request of autonomy by Catalonia.
Above all, we have to consider that the 47,7% of votes for the independence is not the majority. This means that the will to leave Spain is not prevalent in Catalonia. And this is a date, not an opinion.
Considering all, a new Federal Constitution seems the best solution possible.