Be nice.
If it were up to me, I'd have a bunch of brainiacs researching a nice way to kill him (Deniability not an issue). Give me something with a 90% chance and relatively low collateral damage, and I'd go for it. If somebody gave me any cr@p I'd point out that, technically, we're still at war and that this was my notice that the ceasefire was over.
Dunno if that would save Seoul from the artillery parks just north of the parallel, though. Have to wonder who'll follow in his tracks and what they'll do be come the next (fill in the blank) Leader.
But government sponsored assinations are frowned upon. So Kim Jung Il is going to die in a nice palace of old age.