In making the decision of your forum that you want to close, what do you tend to focus on? Winding the shutdown over the course of weeks or months or, do you just close it down immediately?
I think you should wind it down slowly because you never know if someone else would like to take it over.
I know this isn't the same thing, but a couple months ago a friend of mine was going to close his Facebook group that has over 600 members in it. He didn't trust anyone else to take it over... except for me, so now I am running his group. He still checks in and I respect his presence there.
Depends on how long the site's been around. If it's a newer community with not a lot of people, then just suddenly shutting it down probably wouldn't be terrible if things just aren't working out. If it's a more established community with a big userbase that's been around for a while, then making an announcement and winding things down slowly would be the way to go, to allow people to connect with those they want to connect with or get anything they may want to get from the site before it shuts down completely.
I'd rather wind things down than outright shutdown a forum. I know in the past I just shutdown forums whenever I gave up on them but these days I wouldn't do that. This way if someone wants to step up and take over the forum they can.
I’d prefer a shutdown notice with a definitive date to help members prepare. This gives anyone interested in purchasing or taking over the forum time to make an offer to continue the site.
If I were a member and enjoyed the forum, a sudden shutdown would be frustrating. It would also deter me from joining any future websites or forums created by the same person, as I’d see it as a waste of time and always wonder, “Will they shut this down abruptly too?”
When I typically shut down a forum, it's usually because there is no more activity. The activity has usually been absent for several months.
I just shut it down at that point. Everyone has forgotten about the forum, or they would still be posting.
Nowadays, I really try to give my communities a better chance at surviving. I used to close them down really quickly. But now I'm trying to give them a year or two to take off or even just to become a little tight knit community.
But sometimes, a community isn't wanted by your audience or maybe they have already found a community they like and they're super loyal to it. It happens. Sometimes closing the forum down is worth more than keeping it up.