Theories on Belkar's death

[Kish]

Obviously it doesn't make it impossible, however unless Rich is going for a kill-em-all scenario a la Shakespeare, I can't see the story ending with over half the cast dead.

You realize that by moving from "with over half the cast having died at some point" to "with over half the cast dead," Roy no longer counts toward what you're saying, I hope.

Also, I don't honestly think Belkar is interested in murdering V or any other members of the order at this point.

This is based on a fundamental misunderstanding of Belkar, related to the annoying perennial "Belkar's not evil" misunderstanding. Belkar wants to murder nearly everyone he ever interacts with. There is not the slightest indication in the story that Roy and Vaarsuvius have moved away from his hit list since he indicated (his first question to the Oracle) that that's where they were.