I would like to execute a stored procedure, and return immediately back to the script, and the SP shall run in the background until complete, and should not be killed by the PHP process.
How can this be done in PHP?
I believe you can make it work by using mysql events. I haven't tried personally, but it seems like what you are looking for.
You could trigger the execution of a separate PHP script that would run asynchronously (and execute the stored procedure~)