"After neglecting our responsibilities for so long, we will have to ________ sooner or later."

The idiom "face the music" means to confront the consequences of one's actions. This fits the context of having to deal with the repercussions of neglecting responsibilities. 'Take it easy' means to relax or not be overly concerned, which is contrary to the idea of facing consequences. 'Jump the gun' means to start something prematurely, which does not fit the context of dealing with consequences. 'Turn a blind eye' means to ignore something, which is the opposite of confronting the consequences. Face the music is the most appropriate idiom to complete the sentence.