What variety of Dianthus are they? Compact varieties? I would move them into a sheltered spot as they are in containers to prevent them becoming too wet and their roots getting frozen. If they still look good in the spring, then perhaps take cuttings of non-flowering shoots (pips) so you have new plants to eventually take their place.

Depends on whether it is an annual or perennial one. If it is perennial then keep the pots frost free with limited watering. then in the spring give them a trim and or take heel cutting. if its the annual form then it will die but you may get seed from it.