Toyota Repair: Oil changes in 1994 Toyota Tercel, 1994 toyota tercel, toyota tercel

Question
The engine died in my son's 1994 Toyota Tercel.  The car had 45,000 original miles.  I was told by our mechanic this happened because there was no oil.  I was also told there was not an oil leak.  I find this hard to believe because we regularly had the oil changed every 3000 miles. This time the car went 3186 miles since the last oil change - 186 miles over.
Our mechanic wants to replace the engine with a used one for $1,000 including labor & materials.  I am very reluctant to do this because I question if something more is wrong with the car to cause it to use up all the oil. Our mechanic says no - the problem is because we did not change the oil at exactly 3000 miles.  When we bought the car 14 months ago from the original owner, we had our mechanic go over the car & at that time he did repair an oil leak.
Up until this, I have trusted our mechanic/friend completely. Now I am not so sure.  Thank you very much for your help!

Answer
If the engine was low on oil it will cause sever engine damage, regardless of what caused the oil level to become low, the reason this happened is not because you went 168 miles over the 3000 miles, one reason may be that the engine used an exessive amount of oil due to engine wear(which I doubt, considering the mileage) it is more likely that there was an oil leak and the mechanic/friend that you are dealing with doesn't want to admit it because of the previous repair, do yourself a big favor and have someone else look at this to see what caused the engine failure.