Keep the leaves as long as they are green because the plant needs them!

could be either or none of the above. It is hard to tell from the photo, but it could also be sunburn if they were in direct sunlight even with the low temps. If it is sunburn, they will get a grayish tinge on the lower leaves within a day or two. But I definitely don't think 40's was a good idea for plants that were likely used to a constant 70 degrees up until today.

Regardless, I don't think you killed them and likely they will bounce right back with little to no lasting affect.
Bruce

At this point, I'd just leave them be. Overall, they will all recover just fine. If you loose a couple leaves, so be it. But, I wouldn't take action.

I would call that windburn. It's very minor and isn't going to set the plants back. Just don't do it again ;-)