I leave mine in, I have good loamy soil and reasonable drainage and I've only lost the odd one. I can't be doing with the faff of lifting and storage and if I lose one occasionally I don't mind, I can always replace it as they aren't prohibitively expensive.
I leave mine, garden is quite sheltered and in urban Leicester. I do mulch them though. Lost one Bishop of Landaff to the Beast from the East but most survive unscaved.
I'm in Birmingham with very good free draining soil and I've never dug mine up and never lost any.if the slugs get at the young shoots it don't matter as I snip them out when they are about a foot tall
Here in Lincs (clay soil, but improved with horse manure) I lift some and leave some, either in the ground or in pots. Often depends on whether I want to resite them. When I lift them, I knock the soil off, dry them and wrap them in newspaper and leave them in the shed. When I leave them I cover the crown with a big pile of mulch/compost. They seem to survive whatever I do.
Here in West Yorkshire, we kept them in (very large urns) over the winter rather than lifting them. Mistake. We've had plenty of growth this year but only 1 flowering head (as apposed to 8 per urn). Will definitely be lifting within a fortnight and having another go next year.
@Hexagon the urns fairly substantial (300ltr each), so I thought the amount of soil would protect them over the winter. Will empty each urn (keep the spent compost for borders) and store the tubers over winter and go again next year.
I posted this very question on here about this time last year, because most common advice is, lift once frost has blacken the foliage, but there wasnt any frost, then Monty said I believe, if this is the case then lift them on 19th November. I grew about 20 last year, yes some from free seed (another gardening mag!) In past years I have tried, drying them off, hanging them upside down, putting them in sand,putting them in compost, in the dark,shed,garage,greenhouse, none worked. Then I go past a house about half mile away, amazing dahlias 4 feet tall, old chap, invited me in, said hes never lifted them in 8 years, they always come back. So last year I left them in, mulched with home made compost, and put old wicker hanging baskets on top of that Kept my fingers crossed, they did survive, but took a very long time to produce any shoots, I thought they had died, or rotted, dug holes to put in new ones this year,(that I grew on in the greenhouse,) to find they were still there, but started to sprout/shoot very slowly. I am in the SE UK, 10 minutes from the sea.
I pick up 2 or 3 flat cardboard trays from the supermarket and store them in those, a single layer, wrapped in paper. The boxes can then be stacked, saving space until spring, then I open up the paper to let in some light and put them near a window in the spare room, until I can see shoots. Then it's time to take cuttings if I want to and pot them up. Some stay in pots and some get planted out when it has properly warmed up here!
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They wouldn't stand a chance.
Dry cold is very different from wet cold too.
I live in west central Scotland - not where that photo is...