If the wood is still colored (red/brown, etc.) and not a dull gray, then yes, there is a good possibility the top will live. JM's in containers are far more vulnerable to cold damage in winter than those in the ground. Temperatures even in the high 20's can cause damage or even death. It is not unusual for the topgrowth to get some dieback, leaving only the rootstock viable (as it seems in this case) but it is just as likely that the scion portion (or the topgrowth) is just later to leaf out then the rootstock. If/when it does leaf out, you will want to remove that lower growth.

Thanks, for your reply and the info. Much appreciated. Can potted plants be relocated to the garage for the winter? Or a covered patio?

Yes, and yes! When dormant and without foliage, sunlight - or lack of it - is not an issue. Much better to keep safe from cold :-))

my Osakazuki leafs out a little bit at a time.

like gardengal said, if its not gray its probably not dead. wait a few more weeks, it will have more leaves coming out.