well, Thirianna from the Paths series did have her War Mask, being a former DA, and I do assume the other Warlocks have one too - out of sheer necessity... going into battle without one is a singularly bad idea after all, especially for a psyker... But it is more or less explicitly stated as well that Farseers are guys/gals who got "stuck" on the Path of the Seer, later to turn to crystal. So... can one tread that path without a War Mask? I can't recall a reference to anything like "junior" Seers that are no Warlocks...