Actually, this is a topic I've been thinking about grillz recently, thanks to the input of an uninterested friend who knows something about geopolitics in Europe. Indeed, it's one issue that I don't think I've ever seen answered by Catalan independentists. It comes down to a simple problem: would France ever allow an independent Catalan state to be declared on its border?
Before you start immediately by saying "I don't care, they'll just have to accept it", allow me to offer some thoughts. France is one of the two key powers in Europe. It's on the UN Security Council. It's a centre for international diplomacy. Isn't it likely that should France choose to block the establishment of a new state on its borders (and one which, let's face it, would likely have at least some parliamentarians dedicated to the restoration of Catalunya Nord to the Catalan state), is there anything Catalonia could really do? Not being recognised by Spain is of huge importance. Not being recognised by France might be difficult to overcome.
So the question is: What about France? Do you really think France would stand for what it might see as the first of several new states springing up on its borders? Doesn't this gravely affect the independence argument?