If he is one of Hikmatyar's boys, it's no great loss. Hikmatyar is the one that broke the alliance apart back in mid 90's by sending 600 rockets slamming into Kabul.
Hekmatyar has NEVER been part of the Northern Alliance, nor so far as I know have any of the Hzb-i.islami factions. I can't see this as much of a loss.