Ive had many different situations with the summoning dolls. Ive seen them disappear after 20 seconds when standing still <img src="/ubbthreads/images/graemlins/ohh.gif" alt="" /> , some times they are bound to a certain radius from their spawn point (they start flashing red when u go too far) and on other occasions they stick with u till they die (even when entering dungeons etc).
I think the way it is meant to be is that they cant go further than a certain radius from the place they were summoned <img src="/ubbthreads/images/graemlins/stupid.gif" alt="" />