Hi Jche,
As someone who grew up in york,
I wouldn't say its "dead" but it's more of a compact walking/picnic city. It isn’t a huge city with lots of nightlife entertainment like Leeds or Manchester, your social life will largely depend on what you’re into.
Most of your entertainment will be from the uni itself, e.g societies, sports clubs and events so you can always find activities and people to meet through those sessions.
Outside campus there’s lots of pubs, bars, live music spots and quizzes run by the Students’ Union or locally, and lots of low-cost sightseeing like museums (mainly railway), city walks or gardens that are quite nice on a sunny day. There are some well known student night-clubs which everyone will know about, e.g popworld, salvation, etc.
I Hope you enjoy York.