If the Carthaginians win the Battle of the Metaurus and Hasdrubal Barca's reinforcements are able to join up with Hannibal, then Rome is doomed.
After Metaurus however, there is no chance of a permanent Carthaginian comeback, only a mitigation of their defeat.
A very easy PoD to make this happen is to have Hasdrubal's messenger not be captured. There's then good odds that Hasdrubal could well have met up - whether this would have been enough to actually swing the 2nd Punic War back into Carthaginian favour is debatable, but Hannibal with proper siege equipment would have been a significantly more dangerous prospect.
However, that's not the OP's question!
If Hannibal stays in Italy, he has a problem. Between himself and his brother Mago, the Romans are still going to struggle to actually kill him, but in all odds, Carthage would have
had to sue for peace. This means an end to the reinforcements and supplies from Africa. The destruction of Roman Italy, barring Hannibal pulling off
another Trebia/Trasimene/Cannae (although, considering he managed three of the bloody things, that's not impossible...) is now a remote possibility - indeed, one would assume Hannibal might
have to retreat from Italy altogether. Perhaps withdraw back into Spain, or even go into Gaul? Or, for a real wild-card option, Phillip invites them to Macedonia!