My guess is that it'll be situational (ohrly?).

Like, in a Dungeon, you have a sack pull that, after dies, you'll pull the boss. In a mass mob situation, we usualy don't hit IDC combo, just spam HT>RoT or DS, depending of how much time will take for the mob dies, TP management, etc, etc.

In this case, I can see a Dragoon using HT, Blood of Dragoon, RoT, Geirskogul, and than DS, DS, DS... or something like that. This way, we can maximize or DPS and give it time to BoD be available when this mobs dies / next fight begins. Or we could just spam DS until BoD is almost falling, and then Gerskogul, if there would be time for it to come off CD by the time next fight begins.

Anyway, lot's of possibilities.