Cross your fingers?

Try a nice thick mulch, and don't remove it until consistent warm weather.

I've been doing a lot of study on growing grasses lately and I remember reading that to reduce transplant shock, cut off the entire top part of the plant which will alleviate some of the stress. I'd keep them moist and hope for the best come spring. If you run across some on fall sale, you might want to buy them and start over.

I had to take out a miscanthus years ago during fall and I carefully dug it up, balled and burlaped with the dirt still around it, and gave it to a friend who put it straight into the ground and watered it and it didn't come back. It acted just like you are describing.

The issue with dividing or attempting to transplant certain OG's in fall has to do with their growing habits. Miscanthus are warm season grasses, growing and developing root systems during the height of the growing season when both air and soil temps are high. They naturally want to go dormant in fall as colder weather approaches. That means the roots tend to stop growth as well and this will hamper re-establishment if you divide or transplant at this time of year.

I'm not sure if mulching well will help at all -- Donn's comment to "keep your fingers crossed" is about as honest as it gets. Sometimes just being patient is the best course of action :-)

Is this too early in the year to transplant giant miscanthus? I would like to get ahead of the spring rush.

The temperature tomorrow is to be in the 50's and have been in the upper 50's for the past three days.
I want to move them from a full sun location where the frost has gone out.
Cold rain or snow is forcast for Friday and Saturday.

In my opinion, it's way too early, especially in your zone. No matter how nice it is now, you're bound to have at least a couple of months of bad weather ahead. These plants need to be transplanted when they are in active growth, which won't start until April or May.

If you want to get a head start on the season, prepare the new locations.