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
not saying there is prep, just that when you can't actually be killed and are as intelligent as Thanos you should be able to come up with something during the battle. He can use this to take drag the battle out as long as he needs to to have found the answer.