Now, Bassianus and Humphrey are somewhat debatable, as they can conceivably spend part of their "dead" time hidden in a pit or behind bed curtains respectively. However, I have seen both languish on stage in person, so they are included. Conversely, I don't think I've ever seen a Romeo and Juliet production that actually included the "real live body" of Tybalt in the final scene, but I have heard of those that have, and that have similarly had a "real live body" of Caesar in the funeral scene.
If we go by the has-to-be-on-stage-dead-the-entire-time-no-chance-of-being-swapped-out-for-a-dummy matrix, however, the winner is Desdemona. Take a bow Desd-- oh wait, you can't. You're dead.