Here's what I think about where Shtrom is. Shtrom had been hiding in the imperial capital of Earlshide, or somewhere there, all along. Why? The enemies had been able to easily scout the Mc & everyone else since the beginning, even 'rubbing shoulders' directly with MC & whatnot. So I bet he & his closest pawns had been roaming in Earlshide now, if not in the abandoned empire. Why is he letting himself be the sitting duck? Because he isn't. All the demons & beasts that are deployed in the crumbling empire are just the carrots.