The entire point of the Red Wedding is that the death(s) is(are) meant to be a shock. If you kill a character that 50+% of the fanbase expects to be dead at the end of the expansion anyway it wouldn't have anywhere near the same impact.
It would have to be done well though. Vol'jin's sudden death felt really dumb, particularly because Vol'jin had done absolutely nothing since becoming Warchief. It also lost a lot of meaning, and I think got quite a few Horde players disengaged from the lore due to basically playing Warchief Roulette.