There are plenty of little bars and restaurants to go to but they are small and quite laid back, as far as nightlife goes there are probably better places to go if you want to meet new people. If you take a group of friends Niseko is great but imo there will be better options for meeting people and partying. The only women I met when I was there were young girls on family holidays.
It would probably mostly depend on where you stay in town, go for a dorm/lodge style if you want to get to know other people, don't rely on the towns nightlife to provide that.
The snow goes off tho, and it's a huge mountain.