Being the anti-social sod that I am, I'd say stay in I miss loads of stuff with work colleagues and my partners friends, as if I'm not in the mood, if I force it, I, and probably others, have a crappy, miserable time.
I never used to go out with my old workmates either - work nights out are generally full of bitchiness and gossip. I think the only ones that are ever worth going to, are when it's the leaving do of someone you quite liked.