Not necessarily, I suppose it depends on why it has suddenly become long distance? Is it out of necessity, or is perhaps one of the people looking for a little space and perhaps an easy way out? As long as you have the means to visit each other and the trust to wait for each other, there's a chance it can last, although I think the saying 'absence makes the heart grow fonder' is complete nonsense. It certainly requires more commitment to stay in a long-term relationship because you can't just take the other person's presence for granted the way you can when they are with you all the time. It requires more effort to show the other person you are still thinking about them. Above all though, there should be some plan that you will be together again at some point. That's my experience, anyway.