C# Rest Api Cleaning results of long running operations in database

Question

I'm planning to use the so called long running tasks.
I have read best practice articles, and will implement different endpoints for starting, getting status and result of such operations.
Such long running operations will include sql procedures, storing results in tables according to operation Id.
The question is - in what moment should I clear the result, dropping unnecessary data from DB?
I will implement endpont to clear result gracefully, but what if the user simply closes the web page? Should I implement background service cleaning results by timer?
Thanks in advance.