It all depends on why the Entente Cordiale isn't formed. If it is because Declasse and Cambon screw up, or Grey is out of the picture, Britain will likely stay within her splendid isolation most likely trying to curry the favor of the United States. However if it's because Edward VII is shot dead by his would-be Belgian assassin, then it's likely that Britain will opt for some form of alliance framework with Germany since she simply has no other options left, proving the German diplomats correct, which means Britain would have to pay a price for German friendship.