Wow - that's a fun question.
Using the "Resolving Effects" guide.
http://swmgamers.com/SWM/SWM%20Rules%20Main.htmlhttp://swmgamers.com/SWM/Rules/ResolvingEffects.htmlPresumed Dead triggers when his hit points are reduced below 40. This is step 11 of the original attack/ability that reduces Calo Nord to 40 or less, and it interrupts that attack sequence. So queue up the following events that are about to happen:
Last Stand will trigger immediately before Presumed Dead.
Then Presumed Dead will trigger.
Then steps 12-16 of the original attack sequence finish.
Last Stand triggers and Calo Nord takes additional damage, reducing him to 0. Presumed Dead does not trigger on the Grenades damage because it's not the first time his HP goes to 40 or lower. Avoid Defeat does trigger. If he doesn't survive, he is defeated and removed from the Battle Grid, negating Presumed Dead that was going to happen. If he makes his Avoid Defeat save, he's still on the battle grid.
If he survived with Avoid Defeat, then Presumed Dead resolves just like it was going to.
Then resolve the rest of the steps in the original attack.
Note that Presumed Dead triggers on Step 11 of the original attack, potentially negating the defeat from that original attack (which would occur on Step 14 of the original attack). Last Stand triggers before Presumed Dead and it is completely resolved before beginning Presumed Dead. Presumed Dead would resolve before Step 14 of the original attack, but it does not resolve before Step 14 of Presumed Dead's Grenades. So Calo does in fact die from his own Grenades.
Another way to look at it:
Code:
Original Attack (OA)
Steps OA1-10
Step OA11. This character takes damage and Last Stand/Presumed Dead triggers
Last Stand/Grenades (L)
Steps L1-11. This is where Calo damages himself with his own grenades.
Step L12. Avoid Defeat triggers here, which may save him and allow him to still use Presumed Dead.
Also in this step, Last Stand would trigger again, except that Last Stand can only trigger
once per round and it has already triggered at this point.
Steps L14-17. Calo really dies here if Avoid Defeat didn't save him.
Presumed Dead (P)
Steps P1-17. If he died from Last Stand, these steps are never reached.
Steps OA12-17. The character would be defeated by the original attack in these steps, but Presumed Dead prevents it from getting this far.
Short answers to your questions:
1. Yes
2. No. If he is defeated before he uses Presumed Dead, it is canceled.
3. Yes. If he kills himself on his Last Stand, the damage from the Grenades is applied and he is defeated before he gets to resolve Presumed Dead from the original attack.
* 90% sure this interpretation is correct.