I would really disagree with that assessment. In the scene where the lobster gets stabbed, sure there's lots of blood but it only gushes for a second or two, hardly enough time to bleed out and the other scene where alto goes back to the battle scene and throws up, there's an aerial shot of the area and no giant pool of blood and in the following scene where they're packing up the body there's a shot of the ground and still no blood. I don't think the lobster bled out at all.
As for the mikhail sniper shot, the head exploded and fell off. You can see where the shot burned a hole in the head, but the head itself was torn away from the body. The neck cavity shouldn't have been cauterized by that shot.
No, I think the lobsters are like bugs... heads are useful but not exactly necessary for life.