Deer are made to survive harsh winters. They carry heavy coats for warmth, and know how to find browse to feed. Here in Ny I currently have over 3ft of snow. Temp's below 0 for a wk now including a very low 20 below zero Friday night. I've seen deer traveling behind my house, and crossing the local roads. They have trails made for easy movement. They are survivors. What many people don't realize is that the whitetails roughest time of the winter is March. When temps began to rise, using more energy with their still heavy thick coats, and browse is all but gone from eating it all winter. This is when most deer don't make it from the winter months.
We too had a low mast crop in the woods, but fortunately one of my biggested hunting areas was logged very heavy this past spring, and again early fall. That alone hopefully will give them plenty of browse to get through.