Rape and killing by people in power was quite common, though I doubt that it historically happened in this way considering their relative ranks.
If the viceroy had raped and killed a peasant, it would not be surprising, but considering that this was the wife of a scholar, (who did not seem poor or down on his luck). The cost to his reputation and giving his enemies ammunition to use against him would not be worth the cost of one night of pleasure.
I think a more realistic, if less dramatic, route would have been that the viceroy would have invited the scholar to have some poisoned tea. Once the wife is widowed, it is much easier for him to get his way as historically women did not have much power or influence. He would then leverage his position and power to force the woman to be his concubine.
How in the world a viceroy thought it was a good idea to rape and kill someone's wife, leave behind evidence, and then leave that someone alive, I have no idea. All I see is that this viceroy has a death wish and wants to die a painful and horrible death that I quite look forward to seeing.
I wish there wasn't rape, although I am aware it happens, you typically hear of women committing suicide usually by biting their tongue or using a sharp object like a hairpin to commit suicide. Although having the willpower to actually commit suicide is not common. It's just that the rape and killing happened so fast, I feel saddened that it feels like a forced plot point.