Actors without pathgrid can wander without limit
By lingering in a cell for an extended period of time, the player can observe actors without a pathgrid to wander as far from their original location as they like, to the point where they become difficult to find and resetactor command no longer does anything. In vanilla Morrowind actors do not appear to wander further than their specified aiwander radius (in the case of Sjorvar Horse-Mouth it's 512) from their origin point. Furthermore, via the use of the rest/wait function, the game appears to snap them back to origin point at least every 24 hours.
Attached screenshot is of Sjorvar Horse-Mouth, after having wandered very far from his house.