Jacks only hope, in my eyes, is the revelation of what he meant during this exchange:
"Jack, what are you doing here?"
"Well, I've missed our wargames. Haven't you?"
"No, I mean I wasn't supposed to take any casters with me. And I thought you were out of juice anyway."
"Indeed, I am. So I can only conclude I must have used a trick of some sort."
Confirming (for the umpteenth time) that he is out of juice, probably to stop speculation that he might be using Foolamancy.
But why would he come... a caster with no Juice is useless. And he's FAR too valuable for his Side to risk his life so rashly, simply because he "misses wargames."
And what sort of "trick" could he possibly have used? Rob wouldn't throw us that line if it wasn't meant to be explained at some point. Is it some sort of hint?
The only explanations I can think of is:
1) It's not really Jack, but some sort of trick to make Parson THINK it's Jack. I don't like this option, but Jack did
just mysteriously appear, and there are
a gazillion Casters on the other side of the Portal who might be capable of just about anything. But I think Rob has been frustrated with our predictions based on "things are not as they seem" every time Jack is present, and it makes sense to get rid of him in a "what you see is what's really happening" way so we can finally give it up.
2) Jack might know something, some sort of Fate or Prediction or something, that meant he was supposed to die here. Perhaps it was part of the larger plan to spur Parson towards his destiny, so Jack willingly sacrificed himself.