No, and occasionally when HN servers are under strain, and Dang has suggested people log out in order to lighten the load, he has explicitly mentioned not forgetting your password, implying to me that normally people rarely log out or may even create long running throwaway accounts they don't know the password to (I've certainly done this). All that to say I think they would be reticent to force a logout.
E.g. https://news.ycombinator.com/item?id=31027882