How can people not think about that when they bought the rabbit. We got our bunnies in July and it took us two and a half months of research and decision making to decide to have our two as family pets. One of the things we discussed was about winter, in fact we're talking about now, having ordered a thermal hutch cover from the "eBay Man". We're considering ordering the thermal run cover for them as well.
Perhaps it's best if the buns are rehomed, especially, if they can't be bothered with it. With any luck the buns might find a better home.