Has anyone dealt with a derelict recommender?

[Writer]

I am applying to PhD programs, and after three to four months, one of my recommenders still has not issued his recommendations. One of my deadlines is two weeks away, and I am concerned that he simply will not get to it during the holidays. I have, of course, attempted to contact him. At this rate, I do not know if I have enough time to look for an alternate recommender. Has anyone dealt with a situation with a tardy recommender? What happens then?

~Writer~