Thank you for your question.
If the rhubarb leaves are limp and wet looking (exhibiting the appearance of frozen plant material) they should all be carefully removed. It's very likely the oxalic acid from the leaves has been driven down into the leafstalks making them unsafe to eat. When the rhubarb produces new leaves (barring another freeze) they will be fine to use in any of the usual rhubarb recipes. It's safe to place the frozen leaves into the compost pile.
Hope this helps.