If Ghetsis won against Hilbert and Hilda, I'm taking a guess he would become the ruler of Unova, enforcing all sorts of strange laws and unfair rules. There would probably be angry protests and those who did were jailed or killed :/. Sounds grim, but Ghetsis was an evil man with huge ambitious plans so I'm imagining for disobeying him along with Team Plasma results in some horrible punishments.
The Seven Sages would probably replace the gym leaders, banishing them from Unova forever. For the last gym leader, it'd probably be his son, N or one of his trusted members.
As if N, won however I'm sure it wouldn't change. N wasn't like Ghetsis, he was a rather mysterious man, but how he loves Pokemon, he might feel that Pokemon are happy with trainers and stop his ideas. But yeah he might announce it for a few days, before just returning to normal life. That's what I think at least :D.