Well, perhaps. If leaving him alive is sufficient to effectively stabilize Iraq into something approaching a civilized nation, then it's worth it to leave him alive.
Of course, leaving al-Douri alive also leaves open the possibility that he could take over, and reconstitute Iraq along its former Saddamist lines.
It's a finicky trade ... but it's entirely possible that the preponderance of benefit would come from letting the bastard continue to draw breath.
??!?
He’s implicated in gassing the Kurds!