Assigning multiple instant deaths

[Commander Sasha]

A question from my 10yr old has me chasing my head in circles:

 

A Vet with a thunder hammer gets 2 std attacks at S8.

If he hits a unit of 3 Necron scarab swarms T3 W3, and gets lucky so both attacks hit, how many scarab swarms are removed?

i) 1 swarm IDed, then another

ii) Both hits are on the same model, so 1st wound, then 2nd, ID removes last, so only 1 swarm removed,

[Maligoare]

Assuming his luck nets him two successful wound rolls, two scarab swarm bases die, one per unsaved ID-causing wound, as per the bottom right quarter of P26 of the BRB.

[Lord Humongous]

As noted, unsaved instant death causing wounds must always be assigned to an unwounded model if possible, and that model is removed before assigning further unsaved wounds. So not only would the TH remove one scarab swarm per wound it caused, but if there was a wounded scrab base, it would be the LAST one to get instant killed.