I can leave my ivy topiaries(planted in pots) outside all year long, but I'm in Zone 7 and don't know about your zone.

You first must establish that the ivy is a cold hardy variety, even so my ivy that is climbing a tree dies back in the winter in zone 5. I think your best bet in zone 5, if it is a cold hardy variety is to keep it in a pot in a garage, cold frame or cold basement for the winter. Or if you prefer to pot it in the garden create a winter covering by wrapping with straw or leaves and burlap. I overwinter several topiaries in a cold frame packed with leaves.