From the UK facebook rules group:

Dance of the Dead enters the battlefield returning a Clever Impersonator. Clever Impersonator becomes a copy of Jace the Mind Sculptor. What happens to the Clever Impersonator?

Its controller will sacrifice it.

Dance of the Dead's ability returns Clever Impersonator to the battlefield, then attempts to attach the Dance to the Impersonator. Since the Impersonator is not a creature at this point, it's not a legal object for Dance of the Dead to be attached to and that won't happen. The ability continues resolving and sets up a delayed trigger that will go off when the Dance leaves the battlefield.

After that's done, the ability finishes resolving, whereupon SBAs will notice an Aura (Dance of the Dead) sitting on the battlefield unattached and put it into its owner's graveyard. This invokes the aforementioned delayed triggered ability, which upon resolution will cause Clever Impersonator's controller to sacrifice it.