The lilies can stay in the ground. Make sure u CK and see if u have babies from them and get them planted too. U'll find them on the stalk or close to the base of it. Mulch well and will be ready for next yr. Ohh,u said they were growing again..what did u actually mean? New leaves at base or trying to form flowers? @PunkyKy
Your in same zone as me @PunkyKy so you can mulch real well. But depends on if you want to keep them in that bed next year as well. But just mulching real well will be fine to protect from our winters.