Since Ragnaros died in the Firelands, it is unknown if their goal is even possible. Thurgaden believes that at the very least, Grimstone needs to be stopped from brainwashing anyone else and anticipated that the Dark Irons' finest scouts would be sent out to hunt him down.
^ [40-70] Firelands, Anvil-Thane Thurgaden says: This is grave news, <player>. Grimstone and his fanatics workin' tae bring Ragnaros back... Thought he'd know better.
^ [40-70] Firelands, High Justice Grimstone says: Rightful leader? There's nae fire in Moira's veins. Our rightful leader is the true Lord o' Flame, not some Bronzebeard whelp... nor a pretender to his throne.