I think it's going to be played as this.. model "dies", trigger mortal wound roll, brought back to 1 life, "dies" again with excess damage, retriggers mortal wound roll, rest of damage allocated to rest of unit. That seems like the intention and how almost every TO would rule it
But I see why you're saying that the last model can always be brought back because cycle of the storm is triggering after. Just don't think any TO would ever rule it that way nor would anyone want to play anyone trying to do that. The arcanums are clearly not pointed with this way of playing it. Think of how ridiculous an army of arcanums and praetors would be lol.