We know the butcher is already re-cloned in Spireguard(if these vasts work like the clone spell - it happens instantaneously), so it's just a matter of time before he comes back. Why don't we ask
"What is the location of the portal on the material plane that you will use to return to Bluffside from Spireguard."
"If you die, in what location will you re-enter the material plane for the first time after you are brought back to life?"
We can find it and have allies keep it under watch and, possibly, set up an ambush. The Butcher will need to resupply, possibly set up a new clone etc...it could be some time before he returns. Or, if he goes to see Phelix straight from Spireguard, we will get the location of the entrance Phelix uses to access the material plane and we will know that the Butcher will be going straight back to Phelix.
Edit: when the Butcher first returns to the material plane, there will be a high likelihood that he will be carrying his soul object. It needs to be hidden on the material plane for it to work.
I hesitate to ask about the gnome since we don't know if the Butcher knows anything about the personal motivations of the gnome.