Thanks, Berron, glad to see someone's still enjoying it. ;)

monkey3: Let's look at this from several angles. First, the mechanical aspects: the module itself leaves some direct consequences for PCs who choose not to return the phylactery or destroy it.

(1) There's a fourth wave of monsters in the "Streets of Blood" encounter -- those being the undead bonedrinkers.
(2) The Ghostlord is with Kharn in the "Final Battle" encounter, which is meant to significantly raise the EL of the battle.
(3) Even more significant is that if left undealt-with, both Ulwai and Varanthian rejoin the main Red Hand force after the Ghostlord has finished making the bonedrinkers. Presumably Varanthian therefore shows up during the Battle of Brindol, maybe even during the "Streets of Blood" encounter, while Ulwai on RHOD shows up at the "Final Battle" too. Those are big increases on the difficulty levels of those encounters since the players won't have the 15 minute adventuring day open to them as they do in the Thornwaste.

Looking at it from a story perspective, here's my thinking:

(1) It attacks suspension of disbelief to send in undead after the party specifically. The only reason the Ghostlord has been helping the Red Hand is because he thinks the Red Hand has his phylactery and he doesn't know where it is. If you suddenly have phylactery-hunting undead during the Battle of Brindol you'll have the players asking "Huh? How come he didn't recover his phylactery from the Red Hand when they first took it if he knows where it is now?"

(2) Similarly, I wouldn't go with the idea that the Ghostlord "senses" the phylactery in Brindol from some distance away, mostly because, again, he'd be just as likely to start tearing into the Red Hand right there and then -- if they haven't got his phylactery, they have no real hold on him.

(3) But it doesmake sense that the Red Hand sends agents in either before or during the battle to try and recover the phylactery. The Red Hand knows they have to have the phylactery in their possession to control the Ghostlord, so they have to get it back. If it's during the battle maybe Varanthian and Ulwai themselves do the job, since they had the job of looking after the Ghostlord to begin with anyway. If it's before the battle maybe Miha Serani (if she hasn't already been uncovered) figures out the party's got the phylactery and brings in the "assassination squad" of earlier in the adventure to try and recover it. As for how the Hand otherwise detects it: scrying, maybe, or some handwavium that says it's got a magical tracer on it or something.