I live in Zone 8b. I planted a Kumquat Marumi early feb this year. We had a frost a week after I planted it and the temp went down to 20 degrees.
It's not dead. The upper parts have suffered frost damage, but the lower growth looks to be in pretty good condition - you may need to cut back to healthy growth, but if there's a chance of further cold conditions, best to wait till you're sure the risk is gone. Covering with fleece or other protection overnight if there is another very cold spell will help to protect it.