I'm sorry this is too late to help you, and I'm sorry that I don't really have anything useful to help you either! Did you go ahead and try the meatloaf without egg? I would think that if the ground beef is lean enough it would hold together ok without the egg. I read that you can use a few things to substitute for eggs in a recipe, including 2 tablespoons of corn starch, arrowroot flour, or potato starch, or (for cakes) a banana.
I'm glad everything worked out. It's funny, I had already planned on having meatloaf tonight and then I came across your post. Fortunately I have one egg left.