Complex sentence: Meanwhile, Arthas begins to lose his sanity after hearing his forces have been recalled by the Emissary, and he has mercenaries burn his own ships to prevent his men from retreating, then betrays his mercenaries and has his men kill them much to Muradin's disgust.
Split into simpler sentences: Meanwhile, Arthas begins to lose his sanity after hearing his forces have been recalled by the Emissary. Unwilling to return, he has mercenaries burn his own ships to prevent his men from retreating, then betrays the mercenaries and has his men kill them, much to Muradin's disgust.