It does seem to appear that Asmodean was killed by balefire. The real question is, who did it? I don't think it was a Wise One under directions from Morraine. Morraine knew why Rand had him around and appeared to accept it. It appeared to be someone Asmodean knew. I think that rules out Shadar Haran. The other forsaken took SH for a common fade at first and were later surprised by his actions. I lean toward one of the other forsaken.