Let's imagine the following scenario:

The units are within range one of each other, the Rebels don't have a dodge token (and * means hit *! means crit)

My understanding of an attack by the Snowtroopers is that if they roll normally, and the rebels have heavy cover because the Duros is most assuredly behind it. Then the Rebels roll defense normally but the rebels can only lose one figure due to LOS, no matter how many hits get through the defense roll.

Let's say for the sake of argument the Snowtroopers rolled *!, *! and the rebels rolled 2 blanks

The leader figure "dies" but since he has to be the last figure that goes you would actually take off the Duros and put the leader figure in his spot, behind the container. The Snowtroopers cannot kill the entire rebel squad this turn.

No, what if they threw concussion grenades. Blast keyword says it ignores cover.

So the Snowtroopers instead toss grenades at the Rebels. For sake of argument they roll *, * which gets through because blast is ignoring the cover. Again our rebles roll 2 blanks on their white defense dice. Because of the blast keyword is the Duros now a legitimate target? Can the Snowtroopers theoretically kill both rebels even though one is not in LOS? I mean it makes sense, a blast weapon is basically sending a shockwave or shrapnel or something of the sort, which is why it gets around cover.

What do you think?

The snow troopers would only kill the mini in LOS.

Page 32 of the RRG:

Quote

During an attack, if line of sight to a mini in the defender is blocked from all minis in the attacker, that mini in the defender cannot suffer wounds.

Blast only negates dice cancelled from cover, but not having LoS to a mini doesn't fall under cover rules it falls under LoS rules which trump cover.

Additionally, just to clarify, your flamethrower would only provide 1 black dice in this situation since it only has 1 guy in Los (it's one black dice per mini) so beware of Los for special weapons like this.