What if.....

Probably not a lot of difference: much would have depended on whether he'd managed to produce an heir which, given that he was about as straight as Liberace, is unlikely. So even if he had invaded Italy, it is likely that he would have been more interested in the Greek states of Sicily and the south rather than Rome in the centre, his empire would still have been partitioned with those Italian Greek states regaining their independence only to be conquered by Rome some 50 years later as happened IRL.

But I thought Alexander's next conquest would have been Carthage, n'est-pas? Same ultimate result though - North Africa would have been more Hellenised but his empire would still have been partitioned and Carthage would have become another Hellenised successor state like the Seleucids, Antigonids and Ptolemaic Egypt, possibly under a Carthaginian native dynasty rather than a Greek family, but would still fall prey ultimately to Rome before the birth of Jesus...

Just my $0.02

Yours in Christ

Matt