As mentioned above, it depends on what tests the mechanic used to determine the engine is toast. If this engine has some combo of a lot of miles (like 175 k or more) and a history of deferred routine maintenance, the shop’s diagnosis is probably correct. No way to tell via the internet of course, and you always have the option of getting another opinion. But I expect, yes, you’ll need either a major overhaul of this engine, or replace it with another engine, either a used one from a wrecked vehicle, or a remanufactured engine, or a new engine. Of those three options, none are perfect. But all three are worth considering. Which one to chose depends on the condition of other parts of the car, your willingness to spend money on engine repairs, and your other objectives for this car. If you post the model year, the number of miles on the clock, the general condition of the vehicle, any known problems it has, and the routine maintenance history (like the interval on oil and filter changes),you’ll get more specific recommendations here.