Is there a way to estimate consumption of salt when dealing with the boiled meat? I.e. I had 500 grams of meat, boiled in 2 litres of water, with 5 grams of salt diluted in that water. If the water is to be discarded, how much salt will be left in the meat?
Short answer: Not really.
Doing some armchair math, you have two liters of water and 55g of salt, which is about 0.25 liter. That gives you 12.5% the amount salt as there is water in your original solution. The logical solution would be to then cook the meat, then measure the quantity of salt afterwards, right?
That would assume that the absorption and dilution were one-way, i.e.: water-to-meat (as in reverse osmosis to filter water, for instance). In reality, it goes both ways.
The meat, while cooking, will release blood and other body fluids (like oil from the fat) which also contains a certain amount of sodium, and so your post-cooking solution will be "dirty" and that makes it nigh-impossible to get an accurate reading of how much sodium was absorbed vs. released.