Catalan just declared the independence, I hope La Liga allow Barcelona to stick with La Liga, there are many disadvantages if Barcelona decided to join another league if Barcelona join a French league or EPL they should start from the lowest league, and if Catalan make their own league, it's not competitive and they must wait a couple years to join UCL
No other league in European championships, will not invite Barcelona to play. Do you have any idea what this threatens, for example, the French League 1 from FIFA or UEFA ?! They will play in their own championship of Catalonia and make people laugh.
there are some possibilities Barcelona can join another league and I'm sure they will accept it because it will boost their rating, on other hands, there is FC Andorra it's a football club based in Andorra that plays on Spanish league. I'm sure Barcelona will be accepted in La Liga with the change of sports law and the regulation, and I bet Spanish football federation will keep an eye on it since It's respectively beneficial for La Liga and Barcelona