Unfortunately Guy Savoy is only open until 10:30 however they might stay late for parties arriving late assuming they won't rush the dinner.

My choice would be Eiffel Tower at Paris, open until 11:00 pm.

Mix at Mandalay Bay would be nice but I worry that it may be too loud there.

Boa Steakhouse at Caesars and Mon Ami Gabi at Paris are both open till midnight.