Actually, I disagree. All these shots occur simultaneously (by GW law). So if one of two shots kills the model (infantry or vehicle, I don't see the difference) well then he's dead, but the other shot still goes off. It was launched and hit by a model that was, at that moment, still alive.
There has to been precedent for this, people could rapid fire plasma in 5th.
The difference is in the Gets Hot rule for BS-less weapons, as it is determined immediately before you roll To Hit. If a vehicle has two Plasma Cannons, then what? It would seem that the plasma cannons blow up the vehicle before it actually fires, which is different than infantry plasma.
So:
Infantry, Vehicle with a BS using Plasma weapon (ie Razorback with Las/Twin Plasma Gun) - Get Hot check is when you Roll To Hit. You Roll To Hit (firing twice), Getting Hot once, and hitting with the other. You immediately roll your own armor save and fail, killing you/glancing hit. But you have successfully hit, so you are allowed to roll to wound your target.
I cede this, based on the fact that it you've passed the To Hit stage, and can now Roll To Wound. This is even stated "roll to Hit as normal" under Gets Hot.
Infantry, Vehicle without a BS using a Plasma Weapon (ostensibly a Plasma Cannon) - "Roll a d6 immediately before firing". So, how do you fire a blast weapon?
"When firing a Blast weapon, models do not roll To Hit. Instead, just pick one enemy model visible to the firer and place the relevant blast marker with the hole..."
As stated, the act of placing the blast marker counts as firing the weapon. As you roll "immediately before", you make the check before you place the template, ergo it is entirely possible to blow yoursellf up before you shoot.