If it goes into the 40's at night and stays under 60 during the day and the deer isn't in the sun it should be Ok for at least a couple of days like that without any additional ice. During bow season here in Vermont I can usually keep my deer hung up in the soft woods in the shade of some big conifers for 3 days. I just check and if the meat is still cold it is usually good. If it turns warmer than 60 for a good portion of the day I take it home and process it.