This is known as dead weight, and it's the weight of the person at the time he died. The body does not get any lighter or heavier then when the person passed away.
Whether you gain body weight or not is up to you. Typically, smokers who quit have a tendency to put on weight. It's not that the smoking has anything to do with it directly, it's just that the...
They don't: a dead body weighs the same as its normal weight. It seems heavier because if the person is alive, they can balance and help be more convenient to carry.
It depends on the species and condition of the corpse. Let's say it was a squirrel corpse that had its tail bitten off. That wouldn't weigh much, would it? Now let's say that an obese person died of...