Quick Question: If a faceless stalker dies while in a humanoid shape, can it keep the assumed appearance?
The description for its Change Shape ability tells me that it can maintain the new form indefinitely after changing. It also states that it is a swift action to return to its true form, which might sound like there is a small measure of effort involved in changing back, but probably not.
They revert to their true form. the magic that holds them in another form ends at their death.
If this is an issue for your plot, say hello to the Corpse Puppet. It keeps the corpse of anyone who magically assumed a different form inside said false form even after their death, preventing them from ruining any conspiracy they're working for.
(Sure, it's just DC 12 to see through it, but only for "Creatures with reason to suspect deception". Happy arguing about whether there's a reason!)
Ajit Shyama, Shadow Caller, you're a darling. Thank you! Corpse Puppet is exactly what I'm looking for.