There aren't too many bigger Alan Scot fanboys around than me, but honestly Alan goes down after a good battle. The mad Titan can't be killed, he has plenty of prep feats and feats of acquiring source of Omnipotence ( I'm talking IG here not HOTU because that was pure plot and happenstance) I see no way for Alan to put him down to prevent him from eventually finding a power great enough to either take the starheart from Alan (a la Mordru, Ecpliso - let's face it Thanos is a LOT smarter than these guy's) or making Alan doubt himself in some way enough to make him "believe" ( the only way a "full Starheart" Alan has a weakness) he has a weakness Thanos can exploit.
Good battle and it REALLY hurts to say it, but Thanos takes it