Our team has been working hard on an extremely difficult project with an insanely short deadline. We aren't working 80-hour weeks, but the time we are working is stressful to say the least. Everyone is fatigued to some degree and one team member in particular is on the verge of cracking, saying his "heart's not in the project anymore" and his productivity and drive are dwindling rapidly. Unfortunately we can't get the job done without this person (who is definitely not a slacker or someone prone to this type of behavior) so if they or someone else finally breaks we may suffer a failure at a very critical moment. I've been doing my best to keep them (and myself) motivated, but there's only so much I can do before my own productivity begins to fade.
How can I help this one person specifically, and the team at large, to get through this rough time? There are very good things on the horizon if we succeed, but reminding everyone of that has lost its effectiveness in the face of such overwhelming stress.