I found him on the eastern side at 41,83, then ran back to the southern section (slaughterhouse) and found him there as well.  Either there are two abominations named Borgoth in Deatholme, or he respawns extremely quickly, even faster than the other mobs in the area.  If he's not at once place, try the other.

The other 3 lieutenants seem to be stationary.