Hi, welcome to Grows on You. I'm here to give you the good, the bad & the ugly. The dalhias are fine. Just cut off the dried out tops, store the tubers in a cool, dark & dry location until April. The rhubarb however is NOT so forgiving. Mature plants rarely survive transplant. Luckily, it's easy to start new plants from seed indoors then transplant out in a month or so. I hope you are feeling better.

In the UK rhubarb crowns can safely be moved when dormant and I have done it several times with no problems. But don't try it in this cold/wet weather and don't wait until it starts growing. Depending on the weather it might be too late this year but you may be lucky. Remember that you should not use any of the stems the first year after moving to give the plant time to get its roots down.
When storing your dahlias its good to put them in a dry medium such as dry compost, sand etc and to make sure that mice don't get at them!

Are your dahlias in the ground or pots? if in pots knock them out and remove the old compost. if the tubers are firm then you can put them in dry compost frost free until April. Then you can start watering them but keep them frost free.

If in the ground then cut off the dead stuff and depending on how deep they were planted and how cold and wet your garden has been they may well survive. I have 2 that have come up reliably for the last 4 years. But I lost them all in the winters 2010/11.

as for the rhubarb if not in growth move it now. but if it has started to grow then you could but lift as much soil with it as you can and then replant immediately and keep well watered. Or wait until it goes dormant again in the autumn.

Thank you all for the first class advice! xx

If they are in the ground then SBG's advice will do the trick if your soil isn't too heavy or waterlogged. If the soil is light and free-draining, it won't hurt to spread mulch over them to protect the new shoots in early spring from late frosts.