The tubers on the Dahlia are just storage organs, they have no growth points on them, so once they drop off they are dead. Try not to remove any when cleaning up the plants, they are what get the Dahlia growing next year. All the growth points are on the stem of the plant so do not damage that at all.

Just to add to what Owdboggy has said. In order to prevent the tubers shrivelling over winter. Pack round them with multi purpose compost which should help. I've never had a problem with using this method of storage. If any parts of the tuber snap...dust with sulphur powder.....You can of course take cuttings in the early spring....you will get better quality blooms this way.....

PS: Check them periodically over the winter, in case there is any rotting......good luck!!