Just in case the situation comes up, if an Undead warband loses both Vampire and Necromancer, does the entire warband get disbanded, or do only the undead creatures within it "collapse into a piles of bones." Since the Undead player in our campiagn uses only Vampire, Necro, Dregs, and Ghouls (and 1 Dire Wolf), would his warband still continure with a Dreg in charge until a vampire or Necro can be repurchased? Really, neither Dreg nor Ghoul will collapse into dust, but I guess you could argue the Dregs are only around b/c they are servants, and ghouls are just kind of primitive, disorganized things, so without a solid ruler the Dregs and Ghouls would just kind of wander off and do their own thing.
This is one of those cases where actual rule seems to indicate the warband is completely dismissed, but fluff makes it seems like only the undead things go. Since the rulebook frequently mixes fluff in with the rest of the rules and doesn't indicate which is which (except in spell descriptions) this is a weird call.