Is this a usual situation? Suicide is entirely reasonable. He's willing to let himself be a weapon for evil to do what? Have free thoughts sometimes? He'll damn his people and all his allies because he doesn't fancy dying?
Honestly its just another plot hole. Like with everything, the writers didn't think about it.
What they could do however is have him try, but then reveal that while he's not dominated at every moment, he is watched at every moment, and have Zovaal just dominate him if he tried. But since they haven't established that, and seemingly let him act on his own without oversight, it just creates another hole in the plot.