My teenage son failed to listen to my repeated.

My teenage son failed to listen to my repeated advice to change his engine oil every 3000 miles. He bought the vehicle used with approximately 4500 miles. He said he changed the oil at about 30K miles. The vehicle has 43K miles and the check engine light came on. We took it to my trusted local mechanic and he first diagnosed it as a misfire. When he pulled it apart it was apparent the engine was beyond basic repair and was damaged by the lack of routine oil changes. My question is would it be better to replace the engine at a cost of over $3K or sell it for whatever its worth and purchase another vehicle?