I have a route that takes about a minute to run before a response is sent back (this is on purpose). The problem I ran into was when a user logged out after the request was made (via ajax) but before a response was returned, when the response was finally sent back, the user's session would be re-initialized, and stored back into Redis. This was leaving my Redis instance with a lot of extra entries that weren't useful anymore.
My solution was to listen for the req.close event, and when that happened, set a variable that prevented any response from being sent back at all (basically don't call next or res.end). This fixed my problem, but I'm wondering if it is bad to have an unresolved request. I don't actually care what the response is when the request is cancelled, since the user has navigated away from the page that made the request.