At 50 degrees it is still trying to grow but without enough light to supply food it's using up all it's stored energy and will eventually die. If possible I'd suggest putting it outside in a very well protected spot and just let it go dormant. If you can still dig the ground dig a hole and sink the pot right in the soil and cover with mulch. If you have snow already go ahead and bury it in snow. It's the very best in insulation there is. If you want to keep it inside you need to supply it with more light. Even next to a window it won't get enough because of the short days and less intense sunlight. You would need to put it under a light source as well as the window light. And make sure you keep it watered and if possible raise the humidity around it by placing a tray of water next to the pot, not under the pot. Good luck and I hope your rose survives!