Will dahlias rejuvenate from the tubers when dessimated by slugs?

I take it you mean the plants rather than the tubers have been decimated? I'd dig them up carefully now and maybe pot them up if they are still growing leaves or shoots before the autumn ends (as you are in a warmer part of the UK). As they'd already made a lot of growth they should have put a good bit of 'energy' into the tubers, though this would have been better had they been allowed to die down naturally by those dreadful slugs!
They go on growing until late October
you can let them dry out as you normally would and keep them frost free until starting into growth again next year.
Even if they won't regrow now, the tubers should be ok if you dry them out and store them as normal.

provided the slugs havent eaten the dormant buds on the tubers they will be ok. they will need to be kept frost free.