Yeah, the z-space mass is presumably all sloshy in its z-space bag of holding, but it must be still functioning and intact, otherwise they wouldn't be alive in morph. They were inside-out and messed up when their bodies themselves were directly transported out into raw z-space. I think the Yeerk would still be wrapped around the brain, both of them whole, in z-space with the rest of the mass.
If the Controller morpher wasn't morphing something tiny like an ant, but just small enough that say, half of its mass was sent to z-space, at what point would the Yeerk get shifted to z-space with the host brain? As soon as the host brain is changed enough that it's no longer the normal host brain anymore? Or does the brain shift first, since it's in control?
Can a Yeerk ever directly leave a morphed host body, or is it just flatout impossible? Can Visser Three leave his human morph directly? I'd vote for impossible, because we know that morphed Controllers no longer have a vulnerability to Kandrona starvation (I'm thinking about the Yeerk-hawk that Ax lets go in....52? 53?)...and on top of that, it just doesn't make sense, the morpher's brain (along with the host's brain) should be the first thing sent to z-space for protective purposes.
And speaking of brains, now my head really is gonna explode x3