Seems to me Quirrell gets all the same benefits without the vial. As soon as he stages a Bellatrix-sighting or whatever, Moody will arrange for her body to be carefully examined, and the deception will be uncovered. Cue Dumbledore sounding the alarms, etc.
Even assuming it's possible to tell the difference between a few years old rotting corpse and a few years old rotting death doll (magic might help there), Dementors don't care about the dead, and a powerful enough wizard can easily sneak into Azkaban to replace a corpse. Finding a fake corpse in Bellatrix's cell would be a mystery, another conspiracy theory, not a sure signature of Voldemort. It might not convince anyone. Why settle for half-solutions?
Update: Discussion has moved on to a new thread.
After 61 chapters of Harry Potter and the Methods of Rationality and 5 discussion threads with over 500 comments each, HPMOR discussion has graduated from the main page and moved into the Less Wrong discussion section (which seems like a more appropriate location). You can post all of your insights, speculation, and, well, discussion about Eliezer Yudkowsky's Harry Potter fanfic here.
Previous threads are available under the harry_potter tag on the main page (or: one, two, three, four, five); this and future threads will be found under the discussion section tag (since there is a separate tag system for the discussion section). See also the author page for (almost) all things HPMOR, and AdeleneDawner's Author's Notes archive for one thing that the author page is missing.
As a reminder, it's useful to indicate at the start of your comment which chapter you are commenting on. Time passes but your comment stays the same.
Spoiler Warning: this thread is full of spoilers. With few exceptions, spoilers for MOR and canon are fair game to post, without warning or rot13. More specifically: