There’s a reason Pyrrhos picked Sicily over Macedon, it was the easier enterprise. If Pyrrhos had decided to seize Macedon, he would have to face the Galatians as Antigonos did. If he fails and is defeated, he dies and that’s it, no need to dwell on that. If he prevails, he would have to stay in Macedon to keep the throne, otherwise Antigonos would take it. In case he decided to go back to Italy anyway, he would lose at Maleventum all the same, since the conditions for that outcome didn’t change. Considering that Pyrrhos did leave a capable subordinate at Tarentum in OTL, we can tell what would happen once he left Italy, either due to Maleventum or to settle things in Macedon. The Romans, while Pyrrhos is away , would simply take Southern Italy back little by little, until they seize Tarentum. If Pyrrhos came back to Macedon after Maleventum, he’d find his kingdom seized by Antigonos, he’d make the same mistakes and die pretty much the same way. If Pyrrhos had stayed in Macedon, Antigonos would probably profit of any reckless mistake his adversary made while also painting Pyrrhos as a Molossian princeling undeserving to rule the superior Macedonians, and himself as the grandson of Antipatros, nephew of Cassandros and the true heir to Macedon’s throne. In any case Antigonos may not have been an enterprising and courageous general, but he was a smarter king than Pyrrhos, if not a smarter man, he’d probably prevail and Pyrrhos would die all the same.