Yup, pretty sure that's it - when two things happen simultaneously, player whose turn it is decides the order of resolution. Also, I love the lore of Shadow, especially against Orcs and Goblins!
Did somebody mention casting statistics and odds. (subtract mages level from casting cost for accurate odds)
Stats like that make me sad, when I realise how low the percentage chances are of IF on 3 dice AND then Cascading AND then sending my Slann down the hole. And somehow I've managed it twice in the last two games...
So far, the best I see is putting the slann on the side of the unit or in a bunker of saurus you don't really care about. I would love to make my Slann ghostly, but there is a large wood elf meta in my community and their arrows all count as magical ;( Let's do math on that for fun! a unit of 30 trueflight arrows are facing backwards, 8 miles away, behind a mountain and drunk. So, naturally 20 hits on the slann. If the ghostslann is 3" away from an infantry unit, he gets a 4+ look out sir!, 10 hits, wounding on 5's. 3-4 wounds (I'll go with four) then you get your 4+ ward save, which means 2 wounds! I guess he wouldn't die, but I wouldn't risk it.