Acers 'are' deciduous Sharribabe, so expect it to happen at some stage.
Aswell, scratch the bark with your nail .... if it's green underneath then at least they've not died they're just resting.

They are deciduos(spelling!?) so the leaves should of fallen off, unless they did it during summer, which then the cause may be lack of water or sun burn.
a good way to tel is to gently and carefully scrape the bark low down and if its green and 'moist' then it is still alive. If brown and dry then its died.
They dont l ike winter winds so perhaps move it somewhere sheltered if it isnt currenly.

Looks like we were both on the case Bamboo!

Hey, that's not me up there, Nicky, that's Louise - must be the clematis that's confusing you - mine's Niobe, not pink, lol

LOL
Mine's Ville de Lyon :-)))))

Don't threat, mines is bare too , it's normal.

CHEERS GUYS :)