IIRC only the minds are fused together, not the bodies; they all inhabit Zeros body. Lumi mentioned in her diary that she's looking down at her own body. also, if the bodies were gone, the people in ametrine would've mentioned the girls suddenly disappearing, instead of dying. so, them being somehow able to separate wouldn't make sense.
now, another thing i wanted to mention, the remaining PULSE. so far, a single-type Pokemon has become a dual-type (with the exception of muk, who gained the ability Protean instead) when being amplified by the PULSE. i dont quite remember if Mr. Mime was actually confirmed or just a guess as making the force field in labradorra but maybe it wasnt confirmed to be a psychic/fairy as the certain episode was made. the only confirmed time a pokemon (that was definitely a dual-type before release of the episode its mentioned in) was Magneton, which made the PULSE (prototype?) malfunction (also according to the diary, iirc) to "create" ZEL.