I would never underestimate the way fans can motivate players, in any sport. Many individuals need fans to entertain to, the likes of McIlroy has admitted it, Shaun Murphy at the World Championships said it.
However, you cannot ever say 100% that a different result would have happened with fans. In regards to them lot, they were still domestically unbeaten for a good while without fans and has been mentioned, they lost a big game when there were fans.
I love the saying 'no way we were losing' but it is a romantic notion not a factual notion.
In football it can work both ways, as an away team, if you are a confident team then there can easily be a blinkered approach to an away game or the home team, if not confident, can be affected negatively an vice versa (with every permutation in between) . We do not know what would have changed in any game, any team played last season.