In a group with Spain, the playoffs were pretty much a certainty from the beginning.
Now luck will also play some part. It's important for the Italians France and Croatia to win their groups, because those two can still finish second. Portugal seem likely to finish second, but Italy might want them to somehow win the group.
As things stand right now, only Portugal are a very serious opponents in the playoffs. Sweden will be a problem, but the others won't eliminate Italy in 2 legs (Iceland, Northern Ireland, Bosnia, Montenegro, Slovakia). But things can change to worse if Croatia/Turkey finish 2nd in Iceland's group, if Denmark/Poland finish second in Montengro's group, or if France finish second in Sweden's group. It's still most likely that Italy will get a weaker team in the playoffs and qualify for the WC.