Why will the Belksters death be permanent?

[Kish]

Since the oracle tends to give ambiguous answers

Insupportable.

(And please don't point to the strip he spent trolling Belkar as "proof" of this. That was trolling Belkar. The actual fulfillment of the prophecy in question was as straightforward as could be; Belkar caused the death of the Oracle by stabbing him with his daggers.)