I'm willing to guess that your rhizomes are just fine.
I had two that I planted that were 3' and 2' at the end of last fall. They weathered the winter just as yours did (though I actually had to kick them out into the cold half way through
) and both sprouted yesterday after being replanted and subjected to intense fluorescent light (2x 40W bulb 4" away) for 5 days straight.
I would recommend transplanting them while they are dormant. There's more danger to transplanting after they've sprouted.